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Re: [Qemu-devel] [PATCH] hw/char/serial: Only retry if qemu_chr_fe_write
From: |
Paolo Bonzini |
Subject: |
Re: [Qemu-devel] [PATCH] hw/char/serial: Only retry if qemu_chr_fe_write returns 0 |
Date: |
Tue, 5 Jun 2018 11:18:35 +0200 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.7.0 |
On 05/06/2018 09:54, Sergio Lopez wrote:
> Only retry on serial_xmit if qemu_chr_fe_write returns 0, as this is the
> only recoverable error.
>
> Retrying with any other scenario, in addition to being a waste of CPU
> cycles, can compromise the Guest stability if by the vCPU issuing the
> write and the main loop thread are, by chance or explicit pinning,
> running on the same pCPU.
>
> Previous discussion:
>
> https://lists.nongnu.org/archive/html/qemu-devel/2018-05/msg06998.html
>
> Signed-off-by: Sergio Lopez <address@hidden>
> ---
> hw/char/serial.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/hw/char/serial.c b/hw/char/serial.c
> index 605b0d0..6de6c29 100644
> --- a/hw/char/serial.c
> +++ b/hw/char/serial.c
> @@ -260,7 +260,7 @@ static void serial_xmit(SerialState *s)
> if (s->mcr & UART_MCR_LOOP) {
> /* in loopback mode, say that we just received a char */
> serial_receive1(s, &s->tsr, 1);
> - } else if (qemu_chr_fe_write(&s->chr, &s->tsr, 1) != 1 &&
> + } else if (qemu_chr_fe_write(&s->chr, &s->tsr, 1) == 0 &&
> s->tsr_retry < MAX_XMIT_RETRY) {
> assert(s->watch_tag == 0);
> s->watch_tag =
>
Queued, thanks to you and all those who participated in the discussion.
Paolo
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