[Qemu-devel] [PATCH 16/16] aio: push aio_context_acquire/release down to dispatching

[Paolo Bonzini <pbonzini@redhat.com>]

The AioContext data structures are now protected by list_lock and/or
they are walked with FOREACH_RCU primitives.  There is no need anymore
to acquire the AioContext for the entire duration of aio_dispatch.
Instead, just acquire it before and after invoking the callbacks.
The next step is then to push it further down.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 aio-posix.c | 15 ++++++---------
 aio-win32.c | 15 +++++++--------
 async.c     |  2 ++
 3 files changed, 15 insertions(+), 17 deletions(-)

diff --git a/aio-posix.c b/aio-posix.c
index cbdc6e4..015d41a 100644
--- a/aio-posix.c
+++ b/aio-posix.c
@@ -334,7 +334,9 @@ bool aio_dispatch(AioContext *ctx)
         if (!node->deleted &&
             (revents & (G_IO_IN | G_IO_HUP | G_IO_ERR)) &&
             node->io_read) {
+            aio_context_acquire(ctx);
             node->io_read(node->opaque);
+            aio_context_release(ctx);
 
             /* aio_notify() does not count as progress */
             if (node->opaque != &ctx->notifier) {
@@ -344,7 +346,9 @@ bool aio_dispatch(AioContext *ctx)
         if (!node->deleted &&
             (revents & (G_IO_OUT | G_IO_ERR)) &&
             node->io_write) {
+            aio_context_acquire(ctx);
             node->io_write(node->opaque);
+            aio_context_release(ctx);
             progress = true;
         }
 
@@ -360,7 +364,9 @@ bool aio_dispatch(AioContext *ctx)
     qemu_lockcnt_dec(&ctx->list_lock);
 
     /* Run our timers */
+    aio_context_acquire(ctx);
     progress |= timerlistgroup_run_timers(&ctx->tlg);
+    aio_context_release(ctx);
 
     return progress;
 }
@@ -418,7 +424,6 @@ bool aio_poll_internal(AioContext *ctx, bool blocking)
     bool progress;
     int64_t timeout;
 
-    aio_context_acquire(ctx);
     progress = false;
 
     /* aio_notify can avoid the expensive event_notifier_set if
@@ -447,9 +452,6 @@ bool aio_poll_internal(AioContext *ctx, bool blocking)
     timeout = blocking ? aio_compute_timeout(ctx) : 0;
 
     /* wait until next event */
-    if (timeout) {
-        aio_context_release(ctx);
-    }
     if (aio_epoll_check_poll(ctx, pollfds, npfd, timeout)) {
         AioHandler epoll_handler;
 
@@ -464,9 +466,6 @@ bool aio_poll_internal(AioContext *ctx, bool blocking)
     if (blocking) {
         atomic_sub(&ctx->notify_me, 2);
     }
-    if (timeout) {
-        aio_context_acquire(ctx);
-    }
 
     aio_notify_accept(ctx);
 
@@ -485,8 +484,6 @@ bool aio_poll_internal(AioContext *ctx, bool blocking)
         progress = true;
     }
 
-    aio_context_release(ctx);
-
     return progress;
 }
 
diff --git a/aio-win32.c b/aio-win32.c
index 862f48c..7e90dfd 100644
--- a/aio-win32.c
+++ b/aio-win32.c
@@ -245,7 +245,9 @@ static bool aio_dispatch_handlers(AioContext *ctx, HANDLE event)
         if (!node->deleted &&
             (revents || event_notifier_get_handle(node->e) == event) &&
             node->io_notify) {
+            aio_context_acquire(ctx);
             node->io_notify(node->e);
+            aio_context_release(ctx);
 
             /* aio_notify() does not count as progress */
             if (node->e != &ctx->notifier) {
@@ -256,11 +258,15 @@ static bool aio_dispatch_handlers(AioContext *ctx, HANDLE event)
         if (!node->deleted &&
             (node->io_read || node->io_write)) {
             if ((revents & G_IO_IN) && node->io_read) {
+                aio_context_acquire(ctx);
                 node->io_read(node->opaque);
+                aio_context_release(ctx);
                 progress = true;
             }
             if ((revents & G_IO_OUT) && node->io_write) {
+                aio_context_acquire(ctx);
                 node->io_write(node->opaque);
+                aio_context_release(ctx);
                 progress = true;
             }
 
@@ -305,7 +311,6 @@ bool aio_poll_internal(AioContext *ctx, bool blocking)
     int count;
     int timeout;
 
-    aio_context_acquire(ctx);
     progress = false;
 
     /* aio_notify can avoid the expensive event_notifier_set if
@@ -347,17 +352,11 @@ bool aio_poll_internal(AioContext *ctx, bool blocking)
 
         timeout = blocking && !have_select_revents
             ? qemu_timeout_ns_to_ms(aio_compute_timeout(ctx)) : 0;
-        if (timeout) {
-            aio_context_release(ctx);
-        }
         ret = WaitForMultipleObjects(count, events, FALSE, timeout);
         if (blocking) {
             assert(first);
             atomic_sub(&ctx->notify_me, 2);
         }
-        if (timeout) {
-            aio_context_acquire(ctx);
-        }
 
         if (first) {
             aio_notify_accept(ctx);
@@ -380,8 +379,8 @@ bool aio_poll_internal(AioContext *ctx, bool blocking)
         progress |= aio_dispatch_handlers(ctx, event);
     } while (count > 0);
 
+    aio_context_acquire(ctx);
     progress |= timerlistgroup_run_timers(&ctx->tlg);
-
     aio_context_release(ctx);
     return progress;
 }
diff --git a/async.c b/async.c
index bc7e142..9eab833 100644
--- a/async.c
+++ b/async.c
@@ -88,7 +88,9 @@ int aio_bh_poll(AioContext *ctx)
                 ret = 1;
             }
             bh->idle = 0;
+            aio_context_acquire(ctx);
             aio_bh_call(bh);
+            aio_context_release(ctx);
         }
     }
 
-- 
2.5.0