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From 59609c04618734b168df1b751e0126c03671b93c Mon Sep 17 00:00:00 2001
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From: =?UTF-8?q?Marc-Andr=C3=A9=20Lureau?= <marcandre.lureau@redhat.com>
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Date: Fri, 20 Jul 2018 12:17:59 +0200
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Subject: [PATCH 254/268] hw/char/serial: Only retry if qemu_chr_fe_write
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returns 0
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MIME-Version: 1.0
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Content-Type: text/plain; charset=UTF-8
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Content-Transfer-Encoding: 8bit
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RH-Author: Marc-André Lureau <marcandre.lureau@redhat.com>
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Message-id: <20180720121800.18952-2-marcandre.lureau@redhat.com>
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Patchwork-id: 81454
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O-Subject: [RHEL-7.6 qemu-kvm-rhev PATCH v2 1/2] hw/char/serial: Only retry if qemu_chr_fe_write returns 0
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Bugzilla: 1592817
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RH-Acked-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
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RH-Acked-by: Markus Armbruster <armbru@redhat.com>
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RH-Acked-by: John Snow <jsnow@redhat.com>
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From: Sergio Lopez <slp@redhat.com>
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Only retry on serial_xmit if qemu_chr_fe_write returns 0, as this is the
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only recoverable error.
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Retrying with any other scenario, in addition to being a waste of CPU
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cycles, can compromise the Guest stability if by the vCPU issuing the
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write and the main loop thread are, by chance or explicit pinning,
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running on the same pCPU.
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Previous discussion:
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https://lists.nongnu.org/archive/html/qemu-devel/2018-05/msg06998.html
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Signed-off-by: Sergio Lopez <slp@redhat.com>
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Message-Id: <1528185295-14199-1-git-send-email-slp@redhat.com>
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Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
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(cherry picked from commit 019288bf137183bf3407c9824655b753bfafc99f)
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Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
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Signed-off-by: Miroslav Rezanina <mrezanin@redhat.com>
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---
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hw/char/serial.c | 2 +-
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1 file changed, 1 insertion(+), 1 deletion(-)
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diff --git a/hw/char/serial.c b/hw/char/serial.c
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index d6d9b18..d4057bf 100644
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--- a/hw/char/serial.c
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+++ b/hw/char/serial.c
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@@ -262,7 +262,7 @@ static void serial_xmit(SerialState *s)
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if (s->mcr & UART_MCR_LOOP) {
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/* in loopback mode, say that we just received a char */
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serial_receive1(s, &s->tsr, 1);
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- } else if (qemu_chr_fe_write(&s->chr, &s->tsr, 1) != 1 &&
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+ } else if (qemu_chr_fe_write(&s->chr, &s->tsr, 1) == 0 &&
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s->tsr_retry < MAX_XMIT_RETRY) {
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assert(s->watch_tag == 0);
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s->watch_tag =
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--
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1.8.3.1
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