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From 189e720e9fa5536fb22960f158b3b7f91dcccf2c Mon Sep 17 00:00:00 2001
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From: Fam Zheng <famz@redhat.com>
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Date: Tue, 18 Sep 2018 09:07:14 +0200
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Subject: [PATCH 3/3] aio-posix: do skip system call if ctx->notifier polling
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succeeds
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RH-Author: Fam Zheng <famz@redhat.com>
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Message-id: <20180918090714.18069-4-famz@redhat.com>
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Patchwork-id: 82214
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O-Subject: [RHEL-7.6 qemu-kvm-rhev PATCH 3/3] aio-posix: do skip system call if ctx->notifier polling succeeds
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Bugzilla: 1628191
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RH-Acked-by: Paolo Bonzini <pbonzini@redhat.com>
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RH-Acked-by: Jeffrey Cody <jcody@redhat.com>
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RH-Acked-by: Kevin Wolf <kwolf@redhat.com>
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From: Paolo Bonzini <pbonzini@redhat.com>
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Commit 70232b5253 ("aio-posix: Don't count ctx->notifier as progress when
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2018-08-15), by not reporting progress, causes aio_poll to execute the
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system call when polling succeeds because of ctx->notifier. This introduces
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latency before the call to aio_bh_poll() and negates the advantages of
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polling, unfortunately.
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The fix builds on the previous patch, separating the effect of polling on
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the timeout from the progress reported to aio_poll(). ctx->notifier
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does zero the timeout, causing the caller to skip the system call,
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but it does not report progress, so that the bug fix of commit 70232b5253
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still stands.
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Fixes: 70232b5253a3c4e03ed1ac47ef9246a8ac66c6fa
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Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
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Message-Id: <20180912171040.1732-4-pbonzini@redhat.com>
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Reviewed-by: Fam Zheng <famz@redhat.com>
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Signed-off-by: Fam Zheng <famz@redhat.com>
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Signed-off-by: Miroslav Rezanina <mrezanin@redhat.com>
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---
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util/aio-posix.c | 7 ++++---
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1 file changed, 4 insertions(+), 3 deletions(-)
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diff --git a/util/aio-posix.c b/util/aio-posix.c
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index 1b17597..357de8a 100644
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--- a/util/aio-posix.c
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+++ b/util/aio-posix.c
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@@ -498,10 +498,11 @@ static bool run_poll_handlers_once(AioContext *ctx, int64_t *timeout)
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QLIST_FOREACH_RCU(node, &ctx->aio_handlers, node) {
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if (!node->deleted && node->io_poll &&
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aio_node_check(ctx, node->is_external) &&
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- node->io_poll(node->opaque) &&
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- node->opaque != &ctx->notifier) {
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+ node->io_poll(node->opaque)) {
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*timeout = 0;
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- progress = true;
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+ if (node->opaque != &ctx->notifier) {
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+ progress = true;
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+ }
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}
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/* Caller handles freeing deleted nodes. Don't do it here. */
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--
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1.8.3.1
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