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| /freebsd/sys/dev/uart/ |
| H A D | uart_dev_ns8250.c | 39d6144d Fri Aug 12 23:45:17 GMT 2022 Colin Percival <cperciva@FreeBSD.org> ns8250_drain: Drain without DELAY first
In virtual machines with virtual UARTs which have fictitious baud
rates, it may be possible to drain the receive queue very quickly,
without needing to DELAY after each character. Attempt to read
(and discard) the receive queue as fast as possible, stopping for
a DELAY only when LSR_RXRDY is no longer asserted; assume that we
have finished draining the queue when LSR_RXRDY is asserted both
before and after a DELAY.
This speeds up the boot process in FreeBSD/Firecracker by 27 ms.
Reviewed by: imp, jrtc27
Sponsored by: https://www.patreon.com/cperciva
Differential Revision: https://reviews.freebsd.org/D36184
39d6144d Fri Aug 12 23:45:17 GMT 2022 Colin Percival <cperciva@FreeBSD.org> ns8250_drain: Drain without DELAY first
In virtual machines with virtual UARTs which have fictitious baud
rates, it may be possible to drain the receive queue very quickly,
without needing to DELAY after each character. Attempt to read
(and discard) the receive queue as fast as possible, stopping for
a DELAY only when LSR_RXRDY is no longer asserted; assume that we
have finished draining the queue when LSR_RXRDY is asserted both
before and after a DELAY.
This speeds up the boot process in FreeBSD/Firecracker by 27 ms.
Reviewed by: imp, jrtc27
Sponsored by: https://www.patreon.com/cperciva
Differential Revision: https://reviews.freebsd.org/D36184
39d6144d Fri Aug 12 23:45:17 GMT 2022 Colin Percival <cperciva@FreeBSD.org> ns8250_drain: Drain without DELAY first
In virtual machines with virtual UARTs which have fictitious baud
rates, it may be possible to drain the receive queue very quickly,
without needing to DELAY after each character. Attempt to read
(and discard) the receive queue as fast as possible, stopping for
a DELAY only when LSR_RXRDY is no longer asserted; assume that we
have finished draining the queue when LSR_RXRDY is asserted both
before and after a DELAY.
This speeds up the boot process in FreeBSD/Firecracker by 27 ms.
Reviewed by: imp, jrtc27
Sponsored by: https://www.patreon.com/cperciva
Differential Revision: https://reviews.freebsd.org/D36184
39d6144d Fri Aug 12 23:45:17 GMT 2022 Colin Percival <cperciva@FreeBSD.org> ns8250_drain: Drain without DELAY first
In virtual machines with virtual UARTs which have fictitious baud
rates, it may be possible to drain the receive queue very quickly,
without needing to DELAY after each character. Attempt to read
(and discard) the receive queue as fast as possible, stopping for
a DELAY only when LSR_RXRDY is no longer asserted; assume that we
have finished draining the queue when LSR_RXRDY is asserted both
before and after a DELAY.
This speeds up the boot process in FreeBSD/Firecracker by 27 ms.
Reviewed by: imp, jrtc27
Sponsored by: https://www.patreon.com/cperciva
Differential Revision: https://reviews.freebsd.org/D36184
39d6144d Fri Aug 12 23:45:17 GMT 2022 Colin Percival <cperciva@FreeBSD.org> ns8250_drain: Drain without DELAY first
In virtual machines with virtual UARTs which have fictitious baud
rates, it may be possible to drain the receive queue very quickly,
without needing to DELAY after each character. Attempt to read
(and discard) the receive queue as fast as possible, stopping for
a DELAY only when LSR_RXRDY is no longer asserted; assume that we
have finished draining the queue when LSR_RXRDY is asserted both
before and after a DELAY.
This speeds up the boot process in FreeBSD/Firecracker by 27 ms.
Reviewed by: imp, jrtc27
Sponsored by: https://www.patreon.com/cperciva
Differential Revision: https://reviews.freebsd.org/D36184
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