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