Rename "QEMU global mutex" to "BQL" in comments and docs

The term "QEMU global mutex" is identical to the more widely used Big
QEMU Lock ("BQL"). Update the code comments and documentation to use
"B

Rename "QEMU global mutex" to "BQL" in comments and docs

The term "QEMU global mutex" is identical to the more widely used Big
QEMU Lock ("BQL"). Update the code comments and documentation to use
"BQL" instead of "QEMU global mutex".

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Acked-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Paul Durrant <paul@xen.org>
Reviewed-by: Akihiko Odaki <akihiko.odaki@daynix.com>
Reviewed-by: Cédric Le Goater <clg@kaod.org>
Reviewed-by: Harsh Prateek Bora <harshpb@linux.ibm.com>
Message-id: 20240102153529.486531-6-stefanha@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

show more ...

virtio-scsi: don't lock AioContext around virtio_queue_aio_attach_host_notifier()

virtio_queue_aio_attach_host_notifier() does not require the AioContext
lock. Stop taking the lock and add an explic

virtio-scsi: don't lock AioContext around virtio_queue_aio_attach_host_notifier()

virtio_queue_aio_attach_host_notifier() does not require the AioContext
lock. Stop taking the lock and add an explicit smp_wmb() because we were
relying on the implicit barrier in the AioContext lock before.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Message-ID: <20231204164259.1515217-3-stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

show more ...

hw/virtio: Remove unnecessary 'virtio-access.h' header

None of these files use the VirtIO Load/Store API declared
by "hw/virtio/virtio-access.h". This header probably crept
in via copy/pasting, remo

hw/virtio: Remove unnecessary 'virtio-access.h' header

None of these files use the VirtIO Load/Store API declared
by "hw/virtio/virtio-access.h". This header probably crept
in via copy/pasting, remove it.

Note, "virtio-access.h" is target-specific, so any file
including it also become tainted as target-specific.

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Acked-by: Richard Henderson <richard.henderson@linaro.org>
Tested-by: Thomas Huth <thuth@redhat.com>
Message-Id: <20230524093744.88442-10-philmd@linaro.org>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>

show more ...

virtio-scsi: implement BlockDevOps->drained_begin()

The virtio-scsi Host Bus Adapter provides access to devices on a SCSI
bus. Those SCSI devices typically have a BlockBackend. When the
BlockBackend

virtio-scsi: implement BlockDevOps->drained_begin()

The virtio-scsi Host Bus Adapter provides access to devices on a SCSI
bus. Those SCSI devices typically have a BlockBackend. When the
BlockBackend enters a drained section, the SCSI device must temporarily
stop submitting new I/O requests.

Implement this behavior by temporarily stopping virtio-scsi virtqueue
processing when one of the SCSI devices enters a drained section. The
new scsi_device_drained_begin() API allows scsi-disk to message the
virtio-scsi HBA.

scsi_device_drained_begin() uses a drain counter so that multiple SCSI
devices can have overlapping drained sections. The HBA only sees one
pair of .drained_begin/end() calls.

After this commit, virtio-scsi no longer depends on hw/virtio's
ioeventfd aio_set_event_notifier(is_external=true). This commit is a
step towards removing the aio_disable_external() API.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-Id: <20230516190238.8401-19-stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

show more ...

virtio: make it possible to detach host notifier from any thread

virtio_queue_aio_detach_host_notifier() does two things:
1. It removes the fd handler from the event loop.
2. It processes the virtqu

virtio: make it possible to detach host notifier from any thread

virtio_queue_aio_detach_host_notifier() does two things:
1. It removes the fd handler from the event loop.
2. It processes the virtqueue one last time.

The first step can be peformed by any thread and without taking the
AioContext lock.

The second step may need the AioContext lock (depending on the device
implementation) and runs in the thread where request processing takes
place. virtio-blk and virtio-scsi therefore call
virtio_queue_aio_detach_host_notifier() from a BH that is scheduled in
AioContext.

The next patch will introduce a .drained_begin() function that needs to
call virtio_queue_aio_detach_host_notifier(). .drained_begin() functions
cannot call aio_poll() to wait synchronously for the BH. It is possible
for a .drained_poll() callback to asynchronously wait for the BH, but
that is more complex than necessary here.

Move the virtqueue processing out to the callers of
virtio_queue_aio_detach_host_notifier() so that the function can be
called from any thread. This is in preparation for the next patch.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-Id: <20230516190238.8401-17-stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

show more ...

aio-wait: avoid AioContext lock in aio_wait_bh_oneshot()

There is no need for the AioContext lock in aio_wait_bh_oneshot().
It's easy to remove the lock from existing callers and then switch from
AI

aio-wait: avoid AioContext lock in aio_wait_bh_oneshot()

There is no need for the AioContext lock in aio_wait_bh_oneshot().
It's easy to remove the lock from existing callers and then switch from
AIO_WAIT_WHILE() to AIO_WAIT_WHILE_UNLOCKED() in aio_wait_bh_oneshot().

Document that the AioContext lock should not be held across
aio_wait_bh_oneshot(). Holding a lock across aio_poll() can cause
deadlock so we don't want callers to do that.

This is a step towards getting rid of the AioContext lock.

Cc: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-Id: <20230404153307.458883-1-stefanha@redhat.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

show more ...

aio-wait: avoid AioContext lock in aio_wait_bh_oneshot()

There is no need for the AioContext lock in aio_wait_bh_oneshot().
It's easy to remove the lock from existing callers and then switch from
AI

aio-wait: avoid AioContext lock in aio_wait_bh_oneshot()

There is no need for the AioContext lock in aio_wait_bh_oneshot().
It's easy to remove the lock from existing callers and then switch from
AIO_WAIT_WHILE() to AIO_WAIT_WHILE_UNLOCKED() in aio_wait_bh_oneshot().

Document that the AioContext lock should not be held across
aio_wait_bh_oneshot(). Holding a lock across aio_poll() can cause
deadlock so we don't want callers to do that.

This is a step towards getting rid of the AioContext lock.

Cc: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-Id: <20230404153307.458883-1-stefanha@redhat.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

show more ...

virtio-scsi: fix race in virtio_scsi_dataplane_start()

As soon as virtio_scsi_data_plane_start() attaches host notifiers the
IOThread may start virtqueue processing. There is a race between
IOThread

virtio-scsi: fix race in virtio_scsi_dataplane_start()

As soon as virtio_scsi_data_plane_start() attaches host notifiers the
IOThread may start virtqueue processing. There is a race between
IOThread virtqueue processing and virtio_scsi_data_plane_start() because
it only assigns s->dataplane_started after attaching host notifiers.

When a virtqueue handler function in the IOThread calls
virtio_scsi_defer_to_dataplane() it may see !s->dataplane_started and
attempt to start dataplane even though we're already in the IOThread:

#0 0x00007f67b360857c __pthread_kill_implementation (libc.so.6 + 0xa257c)
#1 0x00007f67b35bbd56 raise (libc.so.6 + 0x55d56)
#2 0x00007f67b358e833 abort (libc.so.6 + 0x28833)
#3 0x00007f67b358e75b __assert_fail_base.cold (libc.so.6 + 0x2875b)
#4 0x00007f67b35b4cd6 __assert_fail (libc.so.6 + 0x4ecd6)
#5 0x000055ca87fd411b memory_region_transaction_commit (qemu-kvm + 0x67511b)
#6 0x000055ca87e17811 virtio_pci_ioeventfd_assign (qemu-kvm + 0x4b8811)
#7 0x000055ca87e14836 virtio_bus_set_host_notifier (qemu-kvm + 0x4b5836)
#8 0x000055ca87f8e14e virtio_scsi_set_host_notifier (qemu-kvm + 0x62f14e)
#9 0x000055ca87f8dd62 virtio_scsi_dataplane_start (qemu-kvm + 0x62ed62)
#10 0x000055ca87e14610 virtio_bus_start_ioeventfd (qemu-kvm + 0x4b5610)
#11 0x000055ca87f8c29a virtio_scsi_handle_ctrl (qemu-kvm + 0x62d29a)
#12 0x000055ca87fa5902 virtio_queue_host_notifier_read (qemu-kvm + 0x646902)
#13 0x000055ca882c099e aio_dispatch_handler (qemu-kvm + 0x96199e)
#14 0x000055ca882c1761 aio_poll (qemu-kvm + 0x962761)
#15 0x000055ca880e1052 iothread_run (qemu-kvm + 0x782052)
#16 0x000055ca882c562a qemu_thread_start (qemu-kvm + 0x96662a)

This patch assigns s->dataplane_started before attaching host notifiers
so that virtqueue handler functions that run in the IOThread before
virtio_scsi_data_plane_start() returns correctly identify that dataplane
does not need to be started. This fix is taken from the virtio-blk
dataplane code and it's worth adding a comment in virtio-blk as well to
explain why it works.

Note that s->dataplane_started does not need the AioContext lock because
it is set before attaching host notifiers and cleared after detaching
host notifiers. In other words, the IOThread always sees the value true
and the main loop thread does not modify it while the IOThread is
active.

Buglink: https://bugzilla.redhat.com/show_bug.cgi?id=2099541
Reported-by: Qing Wang <qinwang@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-Id: <20220808162134.240405-1-stefanha@redhat.com>
Reviewed-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

show more ...

virtio-scsi: fix race in virtio_scsi_dataplane_start()

As soon as virtio_scsi_data_plane_start() attaches host notifiers the
IOThread may start virtqueue processing. There is a race between
IOThread

virtio-scsi: fix race in virtio_scsi_dataplane_start()

As soon as virtio_scsi_data_plane_start() attaches host notifiers the
IOThread may start virtqueue processing. There is a race between
IOThread virtqueue processing and virtio_scsi_data_plane_start() because
it only assigns s->dataplane_started after attaching host notifiers.

When a virtqueue handler function in the IOThread calls
virtio_scsi_defer_to_dataplane() it may see !s->dataplane_started and
attempt to start dataplane even though we're already in the IOThread:

#0 0x00007f67b360857c __pthread_kill_implementation (libc.so.6 + 0xa257c)
#1 0x00007f67b35bbd56 raise (libc.so.6 + 0x55d56)
#2 0x00007f67b358e833 abort (libc.so.6 + 0x28833)
#3 0x00007f67b358e75b __assert_fail_base.cold (libc.so.6 + 0x2875b)
#4 0x00007f67b35b4cd6 __assert_fail (libc.so.6 + 0x4ecd6)
#5 0x000055ca87fd411b memory_region_transaction_commit (qemu-kvm + 0x67511b)
#6 0x000055ca87e17811 virtio_pci_ioeventfd_assign (qemu-kvm + 0x4b8811)
#7 0x000055ca87e14836 virtio_bus_set_host_notifier (qemu-kvm + 0x4b5836)
#8 0x000055ca87f8e14e virtio_scsi_set_host_notifier (qemu-kvm + 0x62f14e)
#9 0x000055ca87f8dd62 virtio_scsi_dataplane_start (qemu-kvm + 0x62ed62)
#10 0x000055ca87e14610 virtio_bus_start_ioeventfd (qemu-kvm + 0x4b5610)
#11 0x000055ca87f8c29a virtio_scsi_handle_ctrl (qemu-kvm + 0x62d29a)
#12 0x000055ca87fa5902 virtio_queue_host_notifier_read (qemu-kvm + 0x646902)
#13 0x000055ca882c099e aio_dispatch_handler (qemu-kvm + 0x96199e)
#14 0x000055ca882c1761 aio_poll (qemu-kvm + 0x962761)
#15 0x000055ca880e1052 iothread_run (qemu-kvm + 0x782052)
#16 0x000055ca882c562a qemu_thread_start (qemu-kvm + 0x96662a)

This patch assigns s->dataplane_started before attaching host notifiers
so that virtqueue handler functions that run in the IOThread before
virtio_scsi_data_plane_start() returns correctly identify that dataplane
does not need to be started. This fix is taken from the virtio-blk
dataplane code and it's worth adding a comment in virtio-blk as well to
explain why it works.

Note that s->dataplane_started does not need the AioContext lock because
it is set before attaching host notifiers and cleared after detaching
host notifiers. In other words, the IOThread always sees the value true
and the main loop thread does not modify it while the IOThread is
active.

Buglink: https://bugzilla.redhat.com/show_bug.cgi?id=2099541
Reported-by: Qing Wang <qinwang@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-Id: <20220808162134.240405-1-stefanha@redhat.com>
Reviewed-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

show more ...

virtio-scsi: fix race in virtio_scsi_dataplane_start()

As soon as virtio_scsi_data_plane_start() attaches host notifiers the
IOThread may start virtqueue processing. There is a race between
IOThread

virtio-scsi: fix race in virtio_scsi_dataplane_start()

As soon as virtio_scsi_data_plane_start() attaches host notifiers the
IOThread may start virtqueue processing. There is a race between
IOThread virtqueue processing and virtio_scsi_data_plane_start() because
it only assigns s->dataplane_started after attaching host notifiers.

When a virtqueue handler function in the IOThread calls
virtio_scsi_defer_to_dataplane() it may see !s->dataplane_started and
attempt to start dataplane even though we're already in the IOThread:

#0 0x00007f67b360857c __pthread_kill_implementation (libc.so.6 + 0xa257c)
#1 0x00007f67b35bbd56 raise (libc.so.6 + 0x55d56)
#2 0x00007f67b358e833 abort (libc.so.6 + 0x28833)
#3 0x00007f67b358e75b __assert_fail_base.cold (libc.so.6 + 0x2875b)
#4 0x00007f67b35b4cd6 __assert_fail (libc.so.6 + 0x4ecd6)
#5 0x000055ca87fd411b memory_region_transaction_commit (qemu-kvm + 0x67511b)
#6 0x000055ca87e17811 virtio_pci_ioeventfd_assign (qemu-kvm + 0x4b8811)
#7 0x000055ca87e14836 virtio_bus_set_host_notifier (qemu-kvm + 0x4b5836)
#8 0x000055ca87f8e14e virtio_scsi_set_host_notifier (qemu-kvm + 0x62f14e)
#9 0x000055ca87f8dd62 virtio_scsi_dataplane_start (qemu-kvm + 0x62ed62)
#10 0x000055ca87e14610 virtio_bus_start_ioeventfd (qemu-kvm + 0x4b5610)
#11 0x000055ca87f8c29a virtio_scsi_handle_ctrl (qemu-kvm + 0x62d29a)
#12 0x000055ca87fa5902 virtio_queue_host_notifier_read (qemu-kvm + 0x646902)
#13 0x000055ca882c099e aio_dispatch_handler (qemu-kvm + 0x96199e)
#14 0x000055ca882c1761 aio_poll (qemu-kvm + 0x962761)
#15 0x000055ca880e1052 iothread_run (qemu-kvm + 0x782052)
#16 0x000055ca882c562a qemu_thread_start (qemu-kvm + 0x96662a)

This patch assigns s->dataplane_started before attaching host notifiers
so that virtqueue handler functions that run in the IOThread before
virtio_scsi_data_plane_start() returns correctly identify that dataplane
does not need to be started. This fix is taken from the virtio-blk
dataplane code and it's worth adding a comment in virtio-blk as well to
explain why it works.

Note that s->dataplane_started does not need the AioContext lock because
it is set before attaching host notifiers and cleared after detaching
host notifiers. In other words, the IOThread always sees the value true
and the main loop thread does not modify it while the IOThread is
active.

Buglink: https://bugzilla.redhat.com/show_bug.cgi?id=2099541
Reported-by: Qing Wang <qinwang@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-Id: <20220808162134.240405-1-stefanha@redhat.com>
Reviewed-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

show more ...

virtio-scsi: fix race in virtio_scsi_dataplane_start()

As soon as virtio_scsi_data_plane_start() attaches host notifiers the
IOThread may start virtqueue processing. There is a race between
IOThread

virtio-scsi: fix race in virtio_scsi_dataplane_start()

As soon as virtio_scsi_data_plane_start() attaches host notifiers the
IOThread may start virtqueue processing. There is a race between
IOThread virtqueue processing and virtio_scsi_data_plane_start() because
it only assigns s->dataplane_started after attaching host notifiers.

When a virtqueue handler function in the IOThread calls
virtio_scsi_defer_to_dataplane() it may see !s->dataplane_started and
attempt to start dataplane even though we're already in the IOThread:

#0 0x00007f67b360857c __pthread_kill_implementation (libc.so.6 + 0xa257c)
#1 0x00007f67b35bbd56 raise (libc.so.6 + 0x55d56)
#2 0x00007f67b358e833 abort (libc.so.6 + 0x28833)
#3 0x00007f67b358e75b __assert_fail_base.cold (libc.so.6 + 0x2875b)
#4 0x00007f67b35b4cd6 __assert_fail (libc.so.6 + 0x4ecd6)
#5 0x000055ca87fd411b memory_region_transaction_commit (qemu-kvm + 0x67511b)
#6 0x000055ca87e17811 virtio_pci_ioeventfd_assign (qemu-kvm + 0x4b8811)
#7 0x000055ca87e14836 virtio_bus_set_host_notifier (qemu-kvm + 0x4b5836)
#8 0x000055ca87f8e14e virtio_scsi_set_host_notifier (qemu-kvm + 0x62f14e)
#9 0x000055ca87f8dd62 virtio_scsi_dataplane_start (qemu-kvm + 0x62ed62)
#10 0x000055ca87e14610 virtio_bus_start_ioeventfd (qemu-kvm + 0x4b5610)
#11 0x000055ca87f8c29a virtio_scsi_handle_ctrl (qemu-kvm + 0x62d29a)
#12 0x000055ca87fa5902 virtio_queue_host_notifier_read (qemu-kvm + 0x646902)
#13 0x000055ca882c099e aio_dispatch_handler (qemu-kvm + 0x96199e)
#14 0x000055ca882c1761 aio_poll (qemu-kvm + 0x962761)
#15 0x000055ca880e1052 iothread_run (qemu-kvm + 0x782052)
#16 0x000055ca882c562a qemu_thread_start (qemu-kvm + 0x96662a)

This patch assigns s->dataplane_started before attaching host notifiers
so that virtqueue handler functions that run in the IOThread before
virtio_scsi_data_plane_start() returns correctly identify that dataplane
does not need to be started. This fix is taken from the virtio-blk
dataplane code and it's worth adding a comment in virtio-blk as well to
explain why it works.

Note that s->dataplane_started does not need the AioContext lock because
it is set before attaching host notifiers and cleared after detaching
host notifiers. In other words, the IOThread always sees the value true
and the main loop thread does not modify it while the IOThread is
active.

Buglink: https://bugzilla.redhat.com/show_bug.cgi?id=2099541
Reported-by: Qing Wang <qinwang@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-Id: <20220808162134.240405-1-stefanha@redhat.com>
Reviewed-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

show more ...

virtio-scsi: don't waste CPU polling the event virtqueue

The virtio-scsi event virtqueue is not emptied by its handler function.
This is typical for rx virtqueues where the device uses buffers when

virtio-scsi: don't waste CPU polling the event virtqueue

The virtio-scsi event virtqueue is not emptied by its handler function.
This is typical for rx virtqueues where the device uses buffers when
some event occurs (e.g. a packet is received, an error condition
happens, etc).

Polling non-empty virtqueues wastes CPU cycles. We are not waiting for
new buffers to become available, we are waiting for an event to occur,
so it's a misuse of CPU resources to poll for buffers.

Introduce the new virtio_queue_aio_attach_host_notifier_no_poll() API,
which is identical to virtio_queue_aio_attach_host_notifier() except
that it does not poll the virtqueue.

Before this patch the following command-line consumed 100% CPU in the
IOThread polling and calling virtio_scsi_handle_event():

$ qemu-system-x86_64 -M accel=kvm -m 1G -cpu host \
--object iothread,id=iothread0 \
--device virtio-scsi-pci,iothread=iothread0 \
--blockdev file,filename=test.img,aio=native,cache.direct=on,node-name=drive0 \
--device scsi-hd,drive=drive0

After this patch CPU is no longer wasted.

Reported-by: Nir Soffer <nsoffer@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Tested-by: Nir Soffer <nsoffer@redhat.com>
Message-id: 20220427143541.119567-3-stefanha@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

show more ...

virtio-scsi: don't waste CPU polling the event virtqueue

The virtio-scsi event virtqueue is not emptied by its handler function.
This is typical for rx virtqueues where the device uses buffers when

virtio-scsi: don't waste CPU polling the event virtqueue

The virtio-scsi event virtqueue is not emptied by its handler function.
This is typical for rx virtqueues where the device uses buffers when
some event occurs (e.g. a packet is received, an error condition
happens, etc).

Polling non-empty virtqueues wastes CPU cycles. We are not waiting for
new buffers to become available, we are waiting for an event to occur,
so it's a misuse of CPU resources to poll for buffers.

Introduce the new virtio_queue_aio_attach_host_notifier_no_poll() API,
which is identical to virtio_queue_aio_attach_host_notifier() except
that it does not poll the virtqueue.

Before this patch the following command-line consumed 100% CPU in the
IOThread polling and calling virtio_scsi_handle_event():

$ qemu-system-x86_64 -M accel=kvm -m 1G -cpu host \
--object iothread,id=iothread0 \
--device virtio-scsi-pci,iothread=iothread0 \
--blockdev file,filename=test.img,aio=native,cache.direct=on,node-name=drive0 \
--device scsi-hd,drive=drive0

After this patch CPU is no longer wasted.

Reported-by: Nir Soffer <nsoffer@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Tested-by: Nir Soffer <nsoffer@redhat.com>
Message-id: 20220427143541.119567-3-stefanha@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

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virtio-scsi: don't waste CPU polling the event virtqueue

The virtio-scsi event virtqueue is not emptied by its handler function.
This is typical for rx virtqueues where the device uses buffers when

virtio-scsi: don't waste CPU polling the event virtqueue

The virtio-scsi event virtqueue is not emptied by its handler function.
This is typical for rx virtqueues where the device uses buffers when
some event occurs (e.g. a packet is received, an error condition
happens, etc).

Polling non-empty virtqueues wastes CPU cycles. We are not waiting for
new buffers to become available, we are waiting for an event to occur,
so it's a misuse of CPU resources to poll for buffers.

Introduce the new virtio_queue_aio_attach_host_notifier_no_poll() API,
which is identical to virtio_queue_aio_attach_host_notifier() except
that it does not poll the virtqueue.

Before this patch the following command-line consumed 100% CPU in the
IOThread polling and calling virtio_scsi_handle_event():

$ qemu-system-x86_64 -M accel=kvm -m 1G -cpu host \
--object iothread,id=iothread0 \
--device virtio-scsi-pci,iothread=iothread0 \
--blockdev file,filename=test.img,aio=native,cache.direct=on,node-name=drive0 \
--device scsi-hd,drive=drive0

After this patch CPU is no longer wasted.

Reported-by: Nir Soffer <nsoffer@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Tested-by: Nir Soffer <nsoffer@redhat.com>
Message-id: 20220427143541.119567-3-stefanha@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

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virtio: unify dataplane and non-dataplane ->handle_output()

Now that virtio-blk and virtio-scsi are ready, get rid of
the handle_aio_output() callback. It's no longer needed.

Signed-off-by: Stefan

virtio: unify dataplane and non-dataplane ->handle_output()

Now that virtio-blk and virtio-scsi are ready, get rid of
the handle_aio_output() callback. It's no longer needed.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
Message-id: 20211207132336.36627-7-stefanha@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

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virtio: get rid of VirtIOHandleAIOOutput

The virtqueue host notifier API
virtio_queue_aio_set_host_notifier_handler() polls the virtqueue for new
buffers. AioContext previously required a bool progr

virtio: get rid of VirtIOHandleAIOOutput

The virtqueue host notifier API
virtio_queue_aio_set_host_notifier_handler() polls the virtqueue for new
buffers. AioContext previously required a bool progress return value
indicating whether an event was handled or not. This is no longer
necessary because the AioContext polling API has been split into a poll
check function and an event handler function. The event handler is only
run when we know there is work to do, so it doesn't return bool.

The VirtIOHandleAIOOutput function signature is now the same as
VirtIOHandleOutput. Get rid of the bool return value.

Further simplifications will be made for virtio-blk and virtio-scsi in
the next patch.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
Message-id: 20211207132336.36627-3-stefanha@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

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virtio: Clarify MR transaction optimization

The device model batching its ioeventfds in a single MR transaction is
an optimization. Clarify this in virtio-scsi, virtio-blk and generic
virtio code. A

virtio: Clarify MR transaction optimization

The device model batching its ioeventfds in a single MR transaction is
an optimization. Clarify this in virtio-scsi, virtio-blk and generic
virtio code. Also clarify that the transaction must commit before
closing ioeventfds so that no one is tempted to merge the loops
in the start functions error path and in the stop functions.

Signed-off-by: Greg Kurz <groug@kaod.org>
Message-Id: <162125799728.1394228.339855768563326832.stgit@bahia.lan>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

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virtio-scsi: Configure all host notifiers in a single MR transaction

This allows the virtio-scsi-pci device to batch the setup of all its
host notifiers. This significantly improves boot time of VMs

virtio-scsi: Configure all host notifiers in a single MR transaction

This allows the virtio-scsi-pci device to batch the setup of all its
host notifiers. This significantly improves boot time of VMs with a
high number of vCPUs, e.g. from 6m5.563s down to 1m2.884s for a
pseries machine with 384 vCPUs.

Note that memory_region_transaction_commit() must be called before
virtio_bus_cleanup_host_notifier() because the latter might close
ioeventfds that the transaction still assumes to be around when it
commits.

Signed-off-by: Greg Kurz <groug@kaod.org>
Message-Id: <20210407143501.244343-5-groug@kaod.org>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

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virtio-scsi: Set host notifiers and callbacks separately

Host notifiers are guaranteed to be idle until the callbacks are
hooked up with virtio_queue_aio_set_host_notifier_handler(). They
thus don't

virtio-scsi: Set host notifiers and callbacks separately

Host notifiers are guaranteed to be idle until the callbacks are
hooked up with virtio_queue_aio_set_host_notifier_handler(). They
thus don't need to be set or unset with the AioContext lock held.

Do this outside the critical section, like virtio-blk already
does : basically downgrading virtio_scsi_vring_init() to only
setup the host notifier and set the callback in the caller.

This will allow to batch addition/deletion of ioeventds in
a single memory transaction, which is expected to greatly
improve initialization time.

Signed-off-by: Greg Kurz <groug@kaod.org>
Message-Id: <20210407143501.244343-4-groug@kaod.org>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

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virtio-scsi: don't process IO on fenced dataplane

If virtio_scsi_dataplane_start fails, there is a small window when it drops the
aio lock (in aio_wait_bh_oneshot) and the dataplane's AIO handler ca

virtio-scsi: don't process IO on fenced dataplane

If virtio_scsi_dataplane_start fails, there is a small window when it drops the
aio lock (in aio_wait_bh_oneshot) and the dataplane's AIO handler can
still run during that window.

This is done after the dataplane was marked as fenced, thus we use this flag
to avoid it doing any IO.

Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
Message-Id: <20201217150040.906961-2-mlevitsk@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

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virtio-scsi: don't uninitialize queues that we didn't initialize

Count number of queues that we initialized and only deinitialize these that we
initialized successfully.

Signed-off-by: Maxim Levits

virtio-scsi: don't uninitialize queues that we didn't initialize

Count number of queues that we initialized and only deinitialize these that we
initialized successfully.

Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
Message-Id: <20201217150040.906961-3-mlevitsk@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

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Replace '-enable-kvm' with '-accel kvm' in docs and help texts

The preferred way to select the KVM accelerator is to use "-accel kvm"
these days, so let's be consistent in our documentation and help

Replace '-enable-kvm' with '-accel kvm' in docs and help texts

The preferred way to select the KVM accelerator is to use "-accel kvm"
these days, so let's be consistent in our documentation and help texts.

Signed-off-by: Thomas Huth <thuth@redhat.com>
Message-Id: <1528866321-23886-3-git-send-email-thuth@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

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virtio-scsi: fix race between .ioeventfd_stop() and vq handler

If the main loop thread invokes .ioeventfd_stop() just as the vq handler
function begins in the IOThread then the handler may lose the

virtio-scsi: fix race between .ioeventfd_stop() and vq handler

If the main loop thread invokes .ioeventfd_stop() just as the vq handler
function begins in the IOThread then the handler may lose the race for
the AioContext lock. By the time the vq handler is able to acquire the
AioContext lock the ioeventfd has already been removed and the handler
isn't supposed to run anymore!

Use the new aio_wait_bh_oneshot() function to perform ioeventfd removal
from within the IOThread. This way no races with the vq handler are
possible.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Fam Zheng <famz@redhat.com>
Acked-by: Paolo Bonzini <pbonzini@redhat.com>
Message-id: 20180307144205.20619-4-stefanha@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

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virtio: remove event notifier cleanup call on de-assign

The virtio_bus_set_host_notifier function no longer calls
event_notifier_cleanup when a event notifier is removed.

The commit updates the cod

virtio: remove event notifier cleanup call on de-assign

The virtio_bus_set_host_notifier function no longer calls
event_notifier_cleanup when a event notifier is removed.

The commit updates the code to match the new behavior and calls
virtio_bus_cleanup_host_notifier after the notifier was de-assign
and no longer in use.

This change is a preparation to allow executing the
virtio_bus_set_host_notifier function in a memory region
transaction.

Signed-off-by: Gal Hammer <ghammer@redhat.com>
Reviewed-by: Greg Kurz <groug@kaod.org>
Tested-by: Greg Kurz <groug@kaod.org>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

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scsi: move block/scsi.h to include/scsi/constants.h

Complete the transition by renaming this header, which was
shared by block/iscsi.c and the SCSI emulation code.

Reviewed-by: Philippe Mathieu-Dau

scsi: move block/scsi.h to include/scsi/constants.h

Complete the transition by renaming this header, which was
shared by block/iscsi.c and the SCSI emulation code.

Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

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