Commit 019288bf authored by Sergio Lopez's avatar Sergio Lopez Committed by Paolo Bonzini
Browse files

hw/char/serial: Only retry if qemu_chr_fe_write returns 0 

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: default avatarSergio Lopez <slp@redhat.com>
Message-Id: <1528185295-14199-1-git-send-email-slp@redhat.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent d29a8a1b

hw/char/serial.c

+1 −1
Original line number Diff line number Diff line
@@ -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 =