Hi On Tue, Jun 5, 2018 at 11:18 AM, Paolo Bonzini <pbonz...@redhat.com> wrote: > 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 <s...@redhat.com> >> --- >> 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.
Shouldn't it rety if it returns -1 and the errno == EAGAIN? I am not sure when it would return 0 and a retry would make sense. -- Marc-André Lureau
