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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: Sergio Lopez <slp@redhat.com>
Message-Id: <1528185295-14199-1-git-send-email-slp@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Sergio Lopez 2018-06-05 03:54:55 -04:00 committed by Paolo Bonzini
parent d29a8a1b07
commit 019288bf13
1 changed files with 1 additions and 1 deletions
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2
hw/char/serial.c
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@ -260,7 +260,7 @@ static void serial_xmit(SerialState *s)
if (s->mcr & UART_MCR_LOOP) { if (s->mcr & UART_MCR_LOOP) {
/* in loopback mode, say that we just received a char */ /* in loopback mode, say that we just received a char */
serial_receive1(s, &s->tsr, 1); 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) { s->tsr_retry < MAX_XMIT_RETRY) {
assert(s->watch_tag == 0); assert(s->watch_tag == 0);
s->watch_tag = s->watch_tag =