From 451a04350505ac3078620cacc1c89389c848e6c5 Mon Sep 17 00:00:00 2001

From: Fam Zheng <famz@redhat.com>

Date: Tue, 18 Sep 2018 09:07:13 +0200

Subject: [PATCH 2/3] aio-posix: compute timeout before polling

RH-Author: Fam Zheng <famz@redhat.com>

Message-id: <20180918090714.18069-3-famz@redhat.com>

Patchwork-id: 82213

O-Subject: [RHEL-7.6 qemu-kvm-rhev PATCH 2/3] aio-posix: compute timeout before polling

Bugzilla: 1628191

RH-Acked-by: Paolo Bonzini <pbonzini@redhat.com>

RH-Acked-by: Jeffrey Cody <jcody@redhat.com>

RH-Acked-by: Kevin Wolf <kwolf@redhat.com>

From: Paolo Bonzini <pbonzini@redhat.com>

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>

Signed-off-by: Miroslav Rezanina <mrezanin@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