util/qht: use striped locks under TSAN

Fixes this tsan crash, easy to reproduce with any large enough program:

$ tests/unit/test-qht
1..2
ThreadSanitizer: CHECK failed: sanitizer_deadlock_detector.

util/qht: use striped locks under TSAN

Fixes this tsan crash, easy to reproduce with any large enough program:

$ tests/unit/test-qht
1..2
ThreadSanitizer: CHECK failed: sanitizer_deadlock_detector.h:67 "((n_all_locks_)) < (((sizeof(all_locks_with_contexts_)/sizeof((all_locks_with_contexts_)[0]))))" (0x40, 0x40) (tid=1821568)
#0 __tsan::CheckUnwind() ../../../../src/libsanitizer/tsan/tsan_rtl.cpp:353 (libtsan.so.2+0x90034)
#1 __sanitizer::CheckFailed(char const*, int, char const*, unsigned long long, unsigned long long) ../../../../src/libsanitizer/sanitizer_common/sanitizer_termination.cpp:86 (libtsan.so.2+0xca555)
#2 __sanitizer::DeadlockDetectorTLS<__sanitizer::TwoLevelBitVector<1ul, __sanitizer::BasicBitVector<unsigned long> > >::addLock(unsigned long, unsigned long, unsigned int) ../../../../src/libsanitizer/sanitizer_common/sanitizer_deadlock_detector.h:67 (libtsan.so.2+0xb3616)
#3 __sanitizer::DeadlockDetectorTLS<__sanitizer::TwoLevelBitVector<1ul, __sanitizer::BasicBitVector<unsigned long> > >::addLock(unsigned long, unsigned long, unsigned int) ../../../../src/libsanitizer/sanitizer_common/sanitizer_deadlock_detector.h:59 (libtsan.so.2+0xb3616)
#4 __sanitizer::DeadlockDetector<__sanitizer::TwoLevelBitVector<1ul, __sanitizer::BasicBitVector<unsigned long> > >::onLockAfter(__sanitizer::DeadlockDetectorTLS<__sanitizer::TwoLevelBitVector<1ul, __sanitizer::BasicBitVector<unsigned long> > >*, unsigned long, unsigned int) ../../../../src/libsanitizer/sanitizer_common/sanitizer_deadlock_detector.h:216 (libtsan.so.2+0xb3616)
#5 __sanitizer::DD::MutexAfterLock(__sanitizer::DDCallback*, __sanitizer::DDMutex*, bool, bool) ../../../../src/libsanitizer/sanitizer_common/sanitizer_deadlock_detector1.cpp:169 (libtsan.so.2+0xb3616)
#6 __tsan::MutexPostLock(__tsan::ThreadState*, unsigned long, unsigned long, unsigned int, int) ../../../../src/libsanitizer/tsan/tsan_rtl_mutex.cpp:200 (libtsan.so.2+0xa3382)
#7 __tsan_mutex_post_lock ../../../../src/libsanitizer/tsan/tsan_interface_ann.cpp:384 (libtsan.so.2+0x76bc3)
#8 qemu_spin_lock /home/cota/src/qemu/include/qemu/thread.h:259 (test-qht+0x44a97)
#9 qht_map_lock_buckets ../util/qht.c:253 (test-qht+0x44a97)
#10 do_qht_iter ../util/qht.c:809 (test-qht+0x45f33)
#11 qht_iter ../util/qht.c:821 (test-qht+0x45f33)
#12 iter_check ../tests/unit/test-qht.c:121 (test-qht+0xe473)
#13 qht_do_test ../tests/unit/test-qht.c:202 (test-qht+0xe473)
#14 qht_test ../tests/unit/test-qht.c:240 (test-qht+0xe7c1)
#15 test_default ../tests/unit/test-qht.c:246 (test-qht+0xe828)
#16 <null> <null> (libglib-2.0.so.0+0x7daed)
#17 <null> <null> (libglib-2.0.so.0+0x7d80a)
#18 <null> <null> (libglib-2.0.so.0+0x7d80a)
#19 g_test_run_suite <null> (libglib-2.0.so.0+0x7dfe9)
#20 g_test_run <null> (libglib-2.0.so.0+0x7e055)
#21 main ../tests/unit/test-qht.c:259 (test-qht+0xd2c6)
#22 __libc_start_call_main ../sysdeps/nptl/libc_start_call_main.h:58 (libc.so.6+0x29d8f)
#23 __libc_start_main_impl ../csu/libc-start.c:392 (libc.so.6+0x29e3f)
#24 _start <null> (test-qht+0xdb44)

Signed-off-by: Emilio Cota <cota@braap.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20230111151628.320011-5-cota@braap.org>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20230124180127.1881110-30-alex.bennee@linaro.org>

show more ...

util/qht: add missing atomic_set(hashes[i])

We forgot to add this one in "a890643958 util/qht: atomically set b->hashes".

Detected with tsan.

Reviewed-by: Richard Henderson <richard.henderson@lina

util/qht: add missing atomic_set(hashes[i])

We forgot to add this one in "a890643958 util/qht: atomically set b->hashes".

Detected with tsan.

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Emilio Cota <cota@braap.org>
Message-Id: <20230111151628.320011-3-cota@braap.org>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20230124180127.1881110-28-alex.bennee@linaro.org>

show more ...

util/qht: use striped locks under TSAN

Fixes this tsan crash, easy to reproduce with any large enough program:

$ tests/unit/test-qht
1..2
ThreadSanitizer: CHECK failed: sanitizer_deadlock_detector.

util/qht: use striped locks under TSAN

Fixes this tsan crash, easy to reproduce with any large enough program:

$ tests/unit/test-qht
1..2
ThreadSanitizer: CHECK failed: sanitizer_deadlock_detector.h:67 "((n_all_locks_)) < (((sizeof(all_locks_with_contexts_)/sizeof((all_locks_with_contexts_)[0]))))" (0x40, 0x40) (tid=1821568)
#0 __tsan::CheckUnwind() ../../../../src/libsanitizer/tsan/tsan_rtl.cpp:353 (libtsan.so.2+0x90034)
#1 __sanitizer::CheckFailed(char const*, int, char const*, unsigned long long, unsigned long long) ../../../../src/libsanitizer/sanitizer_common/sanitizer_termination.cpp:86 (libtsan.so.2+0xca555)
#2 __sanitizer::DeadlockDetectorTLS<__sanitizer::TwoLevelBitVector<1ul, __sanitizer::BasicBitVector<unsigned long> > >::addLock(unsigned long, unsigned long, unsigned int) ../../../../src/libsanitizer/sanitizer_common/sanitizer_deadlock_detector.h:67 (libtsan.so.2+0xb3616)
#3 __sanitizer::DeadlockDetectorTLS<__sanitizer::TwoLevelBitVector<1ul, __sanitizer::BasicBitVector<unsigned long> > >::addLock(unsigned long, unsigned long, unsigned int) ../../../../src/libsanitizer/sanitizer_common/sanitizer_deadlock_detector.h:59 (libtsan.so.2+0xb3616)
#4 __sanitizer::DeadlockDetector<__sanitizer::TwoLevelBitVector<1ul, __sanitizer::BasicBitVector<unsigned long> > >::onLockAfter(__sanitizer::DeadlockDetectorTLS<__sanitizer::TwoLevelBitVector<1ul, __sanitizer::BasicBitVector<unsigned long> > >*, unsigned long, unsigned int) ../../../../src/libsanitizer/sanitizer_common/sanitizer_deadlock_detector.h:216 (libtsan.so.2+0xb3616)
#5 __sanitizer::DD::MutexAfterLock(__sanitizer::DDCallback*, __sanitizer::DDMutex*, bool, bool) ../../../../src/libsanitizer/sanitizer_common/sanitizer_deadlock_detector1.cpp:169 (libtsan.so.2+0xb3616)
#6 __tsan::MutexPostLock(__tsan::ThreadState*, unsigned long, unsigned long, unsigned int, int) ../../../../src/libsanitizer/tsan/tsan_rtl_mutex.cpp:200 (libtsan.so.2+0xa3382)
#7 __tsan_mutex_post_lock ../../../../src/libsanitizer/tsan/tsan_interface_ann.cpp:384 (libtsan.so.2+0x76bc3)
#8 qemu_spin_lock /home/cota/src/qemu/include/qemu/thread.h:259 (test-qht+0x44a97)
#9 qht_map_lock_buckets ../util/qht.c:253 (test-qht+0x44a97)
#10 do_qht_iter ../util/qht.c:809 (test-qht+0x45f33)
#11 qht_iter ../util/qht.c:821 (test-qht+0x45f33)
#12 iter_check ../tests/unit/test-qht.c:121 (test-qht+0xe473)
#13 qht_do_test ../tests/unit/test-qht.c:202 (test-qht+0xe473)
#14 qht_test ../tests/unit/test-qht.c:240 (test-qht+0xe7c1)
#15 test_default ../tests/unit/test-qht.c:246 (test-qht+0xe828)
#16 <null> <null> (libglib-2.0.so.0+0x7daed)
#17 <null> <null> (libglib-2.0.so.0+0x7d80a)
#18 <null> <null> (libglib-2.0.so.0+0x7d80a)
#19 g_test_run_suite <null> (libglib-2.0.so.0+0x7dfe9)
#20 g_test_run <null> (libglib-2.0.so.0+0x7e055)
#21 main ../tests/unit/test-qht.c:259 (test-qht+0xd2c6)
#22 __libc_start_call_main ../sysdeps/nptl/libc_start_call_main.h:58 (libc.so.6+0x29d8f)
#23 __libc_start_main_impl ../csu/libc-start.c:392 (libc.so.6+0x29e3f)
#24 _start <null> (test-qht+0xdb44)

Signed-off-by: Emilio Cota <cota@braap.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20230111151628.320011-5-cota@braap.org>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20230124180127.1881110-30-alex.bennee@linaro.org>

show more ...

util/qht: add missing atomic_set(hashes[i])

We forgot to add this one in "a890643958 util/qht: atomically set b->hashes".

Detected with tsan.

Reviewed-by: Richard Henderson <richard.henderson@lina

util/qht: add missing atomic_set(hashes[i])

We forgot to add this one in "a890643958 util/qht: atomically set b->hashes".

Detected with tsan.

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Emilio Cota <cota@braap.org>
Message-Id: <20230111151628.320011-3-cota@braap.org>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20230124180127.1881110-28-alex.bennee@linaro.org>

show more ...

osdep: Move memalign-related functions to their own header

Move the various memalign-related functions out of osdep.h and into
their own header, which we include only where they are used.
While we'r

osdep: Move memalign-related functions to their own header

Move the various memalign-related functions out of osdep.h and into
their own header, which we include only where they are used.
While we're doing this, add some brief documentation comments.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-id: 20220226180723.1706285-10-peter.maydell@linaro.org

show more ...

qemu/atomic.h: rename atomic_ to qatomic_

clang's C11 atomic_fetch_*() functions only take a C11 atomic type
pointer argument. QEMU uses direct types (int, etc) and this causes a
compiler error when

qemu/atomic.h: rename atomic_ to qatomic_

clang's C11 atomic_fetch_*() functions only take a C11 atomic type
pointer argument. QEMU uses direct types (int, etc) and this causes a
compiler error when a QEMU code calls these functions in a source file
that also included <stdatomic.h> via a system header file:

$ CC=clang CXX=clang++ ./configure ... && make
../util/async.c:79:17: error: address argument to atomic operation must be a pointer to _Atomic type ('unsigned int *' invalid)

Avoid using atomic_*() names in QEMU's atomic.h since that namespace is
used by <stdatomic.h>. Prefix QEMU's APIs with 'q' so that atomic.h
and <stdatomic.h> can co-exist. I checked /usr/include on my machine and
searched GitHub for existing "qatomic_" users but there seem to be none.

This patch was generated using:

$ git grep -h -o '\<atomic\(64\)\?_[a-z0-9_]\+' include/qemu/atomic.h | \
sort -u >/tmp/changed_identifiers
$ for identifier in $(</tmp/changed_identifiers); do
sed -i "s%\<$identifier\>%q$identifier%g" \
$(git grep -I -l "\<$identifier\>")
done

I manually fixed line-wrap issues and misaligned rST tables.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Acked-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <20200923105646.47864-1-stefanha@redhat.com>

show more ...

util/: fix some comment spelling errors

I found that there are many spelling errors in the comments of qemu,
so I used the spellcheck tool to check the spelling errors
and finally found some spellin

util/: fix some comment spelling errors

I found that there are many spelling errors in the comments of qemu,
so I used the spellcheck tool to check the spelling errors
and finally found some spelling errors in the util folder.

Signed-off-by: zhaolichang <zhaolichang@huawei.com>
Reviewed-by: Alex Bennee <alex.bennee@linaro.org>
Message-Id: <20200917075029.313-6-zhaolichang@huawei.com>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>

show more ...

qht: call qemu_spin_destroy for head buckets

Signed-off-by: Emilio G. Cota <cota@braap.org>
Signed-off-by: Robert Foley <robert.foley@linaro.org>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
[A

qht: call qemu_spin_destroy for head buckets

Signed-off-by: Emilio G. Cota <cota@braap.org>
Signed-off-by: Robert Foley <robert.foley@linaro.org>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
[AJB: add implied cota s-o-b c.f. github.com/cota/qemu/tree/tsan @ 1bd1209]
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20200609200738.445-6-robert.foley@linaro.org>
Message-Id: <20200612190237.30436-9-alex.bennee@linaro.org>

show more ...

qht: constify arguments to some internal functions

These functions do not modify their @ht or @bucket arguments.
Constify those arguments.

Signed-off-by: Emilio G. Cota <cota@braap.org>
Signed-off-

qht: constify arguments to some internal functions

These functions do not modify their @ht or @bucket arguments.
Constify those arguments.

Signed-off-by: Emilio G. Cota <cota@braap.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

show more ...

qht: constify qht_statistics_init

Signed-off-by: Emilio G. Cota <cota@braap.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

qht: constify qht_lookup

seqlock_read_begin takes a const param since c04649eeea
("seqlock: constify seqlock_read_begin", 2018-08-23), so
we can constify the entire lookup.

Signed-off-by: Emilio G.

qht: constify qht_lookup

seqlock_read_begin takes a const param since c04649eeea
("seqlock: constify seqlock_read_begin", 2018-08-23), so
we can constify the entire lookup.

Signed-off-by: Emilio G. Cota <cota@braap.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

show more ...

qht: fix comment in qht_bucket_remove_entry

Signed-off-by: Emilio G. Cota <cota@braap.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

qht: drop ht argument from qht iterators

Accessing the HT from an iterator results almost always
in a deadlock. Given that only one qht-internal function
uses this argument, drop it from the interfa

qht: drop ht argument from qht iterators

Accessing the HT from an iterator results almost always
in a deadlock. Given that only one qht-internal function
uses this argument, drop it from the interface.

Suggested-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Emilio G. Cota <cota@braap.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

show more ...

qht: add qht_iter_remove

This currently has no users, but the use case is so common that I
think we must support it.

Note that without the appended we cannot safely remove a set of
elements; a 2-st

qht: add qht_iter_remove

This currently has no users, but the use case is so common that I
think we must support it.

Note that without the appended we cannot safely remove a set of
elements; a 2-step approach (i.e. qht_iter first, keep track of
the to-be-deleted elements, and then a bunch of qht_remove calls)
would be racy, since between the iteration and the removals other
threads might insert additional elements.

Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Emilio G. Cota <cota@braap.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

show more ...

qht: remove unused map param from qht_remove__locked

Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Emilio G. Cota <cota@braap.org>
Signed-off-by: Richard Henderson <richard.hender

qht: remove unused map param from qht_remove__locked

Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Emilio G. Cota <cota@braap.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

show more ...

qsp: QEMU's Synchronization Profiler

The goal of this module is to profile synchronization primitives (i.e.
mutexes, recursive mutexes and condition variables) so that scalability
issues can be quic

qsp: QEMU's Synchronization Profiler

The goal of this module is to profile synchronization primitives (i.e.
mutexes, recursive mutexes and condition variables) so that scalability
issues can be quickly diagnosed.

Sync primitives are profiled by QSP based on the vaddr of the object accessed
as well as the call site (file:line_nr). That means the same object called
from two different call sites will be tracked in separate entries, which
might be reported together or separately (see subsequent commit on
call site coalescing).

Some perf numbers:

Host: Intel(R) Core(TM) i7-6700K CPU @ 4.00GHz
Command: taskset -c 0 tests/atomic_add-bench -d 5 -m

- Before: 54.80 Mops/s
- After: 54.75 Mops/s

That is, a negligible slowdown due to the now indirect call to
qemu_mutex_lock. Note that using a branch instead of an indirect
call introduces a more severe slowdown (53.65 Mops/s, i.e. 2% slowdown).

Enabling the profiler (with -p, added in this series) is more interesting:

- No profiling: 54.75 Mops/s
- W/ profiling: 12.53 Mops/s

That is, a 4.36X slowdown.

We can break down this slowdown by removing the get_clock calls or
the entry lookup:

- No profiling: 54.75 Mops/s
- W/o get_clock: 25.37 Mops/s
- W/o entry lookup: 19.30 Mops/s
- W/ profiling: 12.53 Mops/s

Signed-off-by: Emilio G. Cota <cota@braap.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

show more ...

qht: return existing entry when qht_insert fails

The meaning of "existing" is now changed to "matches in hash and
ht->cmp result". This is saner than just checking the pointer value.

Suggested-by:

qht: return existing entry when qht_insert fails

The meaning of "existing" is now changed to "matches in hash and
ht->cmp result". This is saner than just checking the pointer value.

Suggested-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Emilio G. Cota <cota@braap.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

show more ...

qht: require a default comparison function

qht_lookup now uses the default cmp function. qht_lookup_custom is defined
to retain the old behaviour, that is a cmp function is explicitly provided.

qht

qht: require a default comparison function

qht_lookup now uses the default cmp function. qht_lookup_custom is defined
to retain the old behaviour, that is a cmp function is explicitly provided.

qht_insert will gain use of the default cmp in the next patch.

Note that we move qht_lookup_custom's @func to be the last argument,
which makes the new qht_lookup as simple as possible.
Instead of this (i.e. keeping @func 2nd):
0000000000010750 <qht_lookup>:
10750: 89 d1 mov %edx,%ecx
10752: 48 89 f2 mov %rsi,%rdx
10755: 48 8b 77 08 mov 0x8(%rdi),%rsi
10759: e9 22 ff ff ff jmpq 10680 <qht_lookup_custom>
1075e: 66 90 xchg %ax,%ax

We get:
0000000000010740 <qht_lookup>:
10740: 48 8b 4f 08 mov 0x8(%rdi),%rcx
10744: e9 37 ff ff ff jmpq 10680 <qht_lookup_custom>
10749: 0f 1f 80 00 00 00 00 nopl 0x0(%rax)

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Emilio G. Cota <cota@braap.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

show more ...

Purge uses of banned g_assert_FOO()

We banned use of certain g_assert_FOO() functions outside tests, and
made checkpatch.pl flag them (commit 6e9389563e5). We neglected to
purge existing uses. Do

Purge uses of banned g_assert_FOO()

We banned use of certain g_assert_FOO() functions outside tests, and
made checkpatch.pl flag them (commit 6e9389563e5). We neglected to
purge existing uses. Do that now.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <20180608170231.27912-1-armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: John Snow <jsnow@redhat.com>

show more ...

qht: fix unlock-after-free segfault upon resizing

The old map's bucket locks are being unlocked *after*
that same old map has been passed to RCU for destruction.
This is a bug that can cause a segfa

qht: fix unlock-after-free segfault upon resizing

The old map's bucket locks are being unlocked *after*
that same old map has been passed to RCU for destruction.
This is a bug that can cause a segfault, since there's
no guarantee that the deletion will be deferred (e.g.
there may be no concurrent readers).

The segfault is easily triggered in RHEL6/CentOS6 with qht-test,
particularly on a single-core system or by pinning qht-test
to a single core.

Fix it by unlocking the map's bucket locks right after having
published the new map, and (crucially) before marking the map
for deletion via call_rcu().

While at it, expand qht_do_resize() to atomically do (1) a reset,
(2) a resize, or (3) a reset+resize. This simplifies the calling
code, since the new function (qht_do_resize_reset()) acquires
and releases the buckets' locks.

Note that no qht_do_reset inline is provided, since it would have
no users--qht_reset() already performs a reset without taking
ht->lock.

Reported-by: Peter Maydell <peter.maydell@linaro.org>
Reported-by: Daniel P. Berrange <berrange@redhat.com>
Signed-off-by: Emilio G. Cota <cota@braap.org>
Message-Id: <1475706880-10667-3-git-send-email-cota@braap.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

show more ...

qht: simplify qht_reset_size

Sometimes gcc doesn't pick up the fact that 'new' is properly
set if 'resize == true', which may generate an unnecessary
build warning.

Fix it by removing 'resize' and

qht: simplify qht_reset_size

Sometimes gcc doesn't pick up the fact that 'new' is properly
set if 'resize == true', which may generate an unnecessary
build warning.

Fix it by removing 'resize' and directly checking that 'new'
is non-NULL.

Signed-off-by: Emilio G. Cota <cota@braap.org>
Message-Id: <1475706880-10667-2-git-send-email-cota@braap.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

show more ...

util/qht: atomically set b->hashes

ThreadSanitizer detects a possible race between reading/writing the
hashes. The ordering semantics are already documented for QHT however
for true C11 compliance w

util/qht: atomically set b->hashes

ThreadSanitizer detects a possible race between reading/writing the
hashes. The ordering semantics are already documented for QHT however
for true C11 compliance we should use relaxed atomic primitives for
accesses that are done across threads. On x86 this slightly changes to
the code to not do a load/compare in a single instruction leading to a
slight performance degradation.

Running 'taskset -c 0 tests/qht-bench -n 1 -d 10' (i.e. all lookups) 10
times, we get:

before the patch:
$ ./mean.pl 34.04 34.24 34.38 34.25 34.18 34.51 34.46 34.44 34.29 34.08
34.287 +- 0.160072900059109
after:
$ ./mean.pl 33.94 34.00 33.52 33.46 33.55 33.71 34.27 34.06 34.28 34.58
33.937 +- 0.374731014640279

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Emilio G. Cota <cota@braap.org>
Message-Id: <20160930213106.20186-10-alex.bennee@linaro.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

show more ...

qht: do not segfault when gathering stats from an uninitialized qht

So far, QHT functions assume that the passed qht has previously been
initialized--otherwise they segfault.

This patch makes an ex

qht: do not segfault when gathering stats from an uninitialized qht

So far, QHT functions assume that the passed qht has previously been
initialized--otherwise they segfault.

This patch makes an exception for qht_statistics_init, with the goal
of simplifying calling code. For instance, qht_statistics_init is
called from the 'info jit' dump, and given that under KVM the TB qht
is never initialized, we get a segfault. Thus, instead of complicating
the 'info jit' code with additional checks, let's allow passing an
uninitialized qht to qht_statistics_init.

While at it, add a test for this to test-qht.

Before the patch (for $ qemu -enable-kvm [...]):
(qemu) info jit
[...]
direct jump count 0 (0%) (2 jumps=0 0%)
Program received signal SIGSEGV, Segmentation fault.

After the patch the "TB hash buckets", "TB hash occupancy"
and "TB hash avg chain" lines are omitted.
(qemu) info jit
[...]
direct jump count 0 (0%) (2 jumps=0 0%)
TB hash buckets 0/0 (-nan% head buckets used)
TB hash occupancy nan% avg chain occ. Histogram: (null)
TB hash avg chain nan buckets. Histogram: (null)
[...]

Reported by: Changlong Xie <xiecl.fnst@cn.fujitsu.com>
Signed-off-by: Emilio G. Cota <cota@braap.org>
Message-Id: <1469205390-14369-1-git-send-email-cota@braap.org>
[Extract printing statistics to an entirely separate function. - Paolo]
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

show more ...

util/qht: Document memory ordering assumptions

It is naturally expected that some memory ordering should be provided
around qht_insert() and qht_lookup(). Document these assumptions in the
header fi

util/qht: Document memory ordering assumptions

It is naturally expected that some memory ordering should be provided
around qht_insert() and qht_lookup(). Document these assumptions in the
header file and put some comments in the source to denote how that
memory ordering requirements are fulfilled.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
[Sergey Fedorov: commit title and message provided;
comment on qht_remove() elided]
Signed-off-by: Sergey Fedorov <serge.fdrv@gmail.com>
Message-Id: <20160715175852.30749-2-sergey.fedorov@linaro.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

show more ...

clean-includes: run it once more

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>