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qemu-kvm/SOURCES/kvm-aio-posix-compute-timeout-before-polling.patch

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From 59776df6fa3156a467e889ae00751da4bf6857eb Mon Sep 17 00:00:00 2001
From: Fam Zheng <famz@redhat.com>
Date: Tue, 9 Oct 2018 08:16:50 +0100
Subject: [PATCH 06/17] aio-posix: compute timeout before polling
RH-Author: Fam Zheng <famz@redhat.com>
Message-id: <20181009081651.15463-5-famz@redhat.com>
Patchwork-id: 82453
O-Subject: [RHEL8/rhel qemu-kvm PATCH 4/5] aio-posix: compute timeout before polling
Bugzilla: 1632622
RH-Acked-by: Thomas Huth <thuth@redhat.com>
RH-Acked-by: Stefan Hajnoczi <stefanha@redhat.com>
RH-Acked-by: Danilo de Paula <ddepaula@redhat.com>
From: Paolo Bonzini <pbonzini@redhat.com>
BZ: 1632622
This is a preparation for the next patch, and also a very small
optimization. Compute the timeout only once, before invoking
try_poll_mode, and adjust it in run_poll_handlers. The adjustment
is the polling time when polling fails, or zero (non-blocking) if
polling succeeds.
Fixes: 70232b5253a3c4e03ed1ac47ef9246a8ac66c6fa
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <20180912171040.1732-3-pbonzini@redhat.com>
Reviewed-by: Fam Zheng <famz@redhat.com>
Signed-off-by: Fam Zheng <famz@redhat.com>
(cherry picked from commit e30cffa04d52e35996569f1cfac111be19576bde)
Signed-off-by: Fam Zheng <famz@redhat.com>
Signed-off-by: Danilo C. L. de Paula <ddepaula@redhat.com>
---
util/aio-posix.c | 59 ++++++++++++++++++++++++++++++++-----------------------
util/trace-events | 4 ++--
2 files changed, 36 insertions(+), 27 deletions(-)
diff --git a/util/aio-posix.c b/util/aio-posix.c
index 1d7cc53..1b17597 100644
--- a/util/aio-posix.c
+++ b/util/aio-posix.c
@@ -490,7 +490,7 @@ static void add_pollfd(AioHandler *node)
npfd++;
}
-static bool run_poll_handlers_once(AioContext *ctx)
+static bool run_poll_handlers_once(AioContext *ctx, int64_t *timeout)
{
bool progress = false;
AioHandler *node;
@@ -500,6 +500,7 @@ static bool run_poll_handlers_once(AioContext *ctx)
aio_node_check(ctx, node->is_external) &&
node->io_poll(node->opaque) &&
node->opaque != &ctx->notifier) {
+ *timeout = 0;
progress = true;
}
@@ -522,31 +523,38 @@ static bool run_poll_handlers_once(AioContext *ctx)
*
* Returns: true if progress was made, false otherwise
*/
-static bool run_poll_handlers(AioContext *ctx, int64_t max_ns)
+static bool run_poll_handlers(AioContext *ctx, int64_t max_ns, int64_t *timeout)
{
bool progress;
- int64_t end_time;
+ int64_t start_time, elapsed_time;
assert(ctx->notify_me);
assert(qemu_lockcnt_count(&ctx->list_lock) > 0);
- trace_run_poll_handlers_begin(ctx, max_ns);
-
- end_time = qemu_clock_get_ns(QEMU_CLOCK_REALTIME) + max_ns;
+ trace_run_poll_handlers_begin(ctx, max_ns, *timeout);
+ start_time = qemu_clock_get_ns(QEMU_CLOCK_REALTIME);
do {
- progress = run_poll_handlers_once(ctx);
- } while (!progress && qemu_clock_get_ns(QEMU_CLOCK_REALTIME) < end_time
+ progress = run_poll_handlers_once(ctx, timeout);
+ elapsed_time = qemu_clock_get_ns(QEMU_CLOCK_REALTIME) - start_time;
+ } while (!progress && elapsed_time < max_ns
&& !atomic_read(&ctx->poll_disable_cnt));
- trace_run_poll_handlers_end(ctx, progress);
+ /* If time has passed with no successful polling, adjust *timeout to
+ * keep the same ending time.
+ */
+ if (*timeout != -1) {
+ *timeout -= MIN(*timeout, elapsed_time);
+ }
+ trace_run_poll_handlers_end(ctx, progress, *timeout);
return progress;
}
/* try_poll_mode:
* @ctx: the AioContext
- * @blocking: busy polling is only attempted when blocking is true
+ * @timeout: timeout for blocking wait, computed by the caller and updated if
+ * polling succeeds.
*
* ctx->notify_me must be non-zero so this function can detect aio_notify().
*
@@ -554,19 +562,16 @@ static bool run_poll_handlers(AioContext *ctx, int64_t max_ns)
*
* Returns: true if progress was made, false otherwise
*/
-static bool try_poll_mode(AioContext *ctx, bool blocking)
+static bool try_poll_mode(AioContext *ctx, int64_t *timeout)
{
- if (blocking && ctx->poll_max_ns && !atomic_read(&ctx->poll_disable_cnt)) {
- /* See qemu_soonest_timeout() uint64_t hack */
- int64_t max_ns = MIN((uint64_t)aio_compute_timeout(ctx),
- (uint64_t)ctx->poll_ns);
+ /* See qemu_soonest_timeout() uint64_t hack */
+ int64_t max_ns = MIN((uint64_t)*timeout, (uint64_t)ctx->poll_ns);
- if (max_ns) {
- poll_set_started(ctx, true);
+ if (max_ns && !atomic_read(&ctx->poll_disable_cnt)) {
+ poll_set_started(ctx, true);
- if (run_poll_handlers(ctx, max_ns)) {
- return true;
- }
+ if (run_poll_handlers(ctx, max_ns, timeout)) {
+ return true;
}
}
@@ -575,7 +580,7 @@ static bool try_poll_mode(AioContext *ctx, bool blocking)
/* Even if we don't run busy polling, try polling once in case it can make
* progress and the caller will be able to avoid ppoll(2)/epoll_wait(2).
*/
- return run_poll_handlers_once(ctx);
+ return run_poll_handlers_once(ctx, timeout);
}
bool aio_poll(AioContext *ctx, bool blocking)
@@ -605,8 +610,14 @@ bool aio_poll(AioContext *ctx, bool blocking)
start = qemu_clock_get_ns(QEMU_CLOCK_REALTIME);
}
- progress = try_poll_mode(ctx, blocking);
- if (!progress) {
+ timeout = blocking ? aio_compute_timeout(ctx) : 0;
+ progress = try_poll_mode(ctx, &timeout);
+ assert(!(timeout && progress));
+
+ /* If polling is allowed, non-blocking aio_poll does not need the
+ * system call---a single round of run_poll_handlers_once suffices.
+ */
+ if (timeout || atomic_read(&ctx->poll_disable_cnt)) {
assert(npfd == 0);
/* fill pollfds */
@@ -620,8 +631,6 @@ bool aio_poll(AioContext *ctx, bool blocking)
}
}
- timeout = blocking ? aio_compute_timeout(ctx) : 0;
-
/* wait until next event */
if (aio_epoll_check_poll(ctx, pollfds, npfd, timeout)) {
AioHandler epoll_handler;
diff --git a/util/trace-events b/util/trace-events
index 4822434..79569b7 100644
--- a/util/trace-events
+++ b/util/trace-events
@@ -1,8 +1,8 @@
# See docs/devel/tracing.txt for syntax documentation.
# util/aio-posix.c
-run_poll_handlers_begin(void *ctx, int64_t max_ns) "ctx %p max_ns %"PRId64
-run_poll_handlers_end(void *ctx, bool progress) "ctx %p progress %d"
+run_poll_handlers_begin(void *ctx, int64_t max_ns, int64_t timeout) "ctx %p max_ns %"PRId64 " timeout %"PRId64
+run_poll_handlers_end(void *ctx, bool progress, int64_t timeout) "ctx %p progress %d new timeout %"PRId64
poll_shrink(void *ctx, int64_t old, int64_t new) "ctx %p old %"PRId64" new %"PRId64
poll_grow(void *ctx, int64_t old, int64_t new) "ctx %p old %"PRId64" new %"PRId64
--
1.8.3.1
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