From c84bb01c0c56cadb70a95c874b32ed85b8177504 Mon Sep 17 00:00:00 2001
From: tangbinzy <tangbin_yewu@cmss.chinamobile.com>
Date: Tue, 26 Sep 2023 06:41:50 +0000
Subject: [PATCH] thread-pool: optimize scheduling of completion  bottom half
 mainline inclusion commit 3c7b72ddca9ce85a9d1e8a98fd0996b74597b5ae category:
 bugfix

---------------------------------------------------------------

The completion bottom half was scheduled within the pool->lock
critical section.  That actually results in worse performance,
because the worker thread can run its own small critical section
and go to sleep before the bottom half starts running.

Note that this simple change does not produce an improvement without
changing the thread pool QemuSemaphore to a condition variable.

Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Nicolas Saenz Julienne <nsaenzju@redhat.com>
Message-Id: <20220514065012.1149539-2-pbonzini@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

Signed-off-by: tangbinzy <tangbin_yewu@cmss.chinamobile.com>
---
 util/thread-pool.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/util/thread-pool.c b/util/thread-pool.c
index d763cea505..7e9e2c178b 100644
--- a/util/thread-pool.c
+++ b/util/thread-pool.c
@@ -108,9 +108,8 @@ static void *worker_thread(void *opaque)
         smp_wmb();
         req->state = THREAD_DONE;
 
-        qemu_mutex_lock(&pool->lock);
-
         qemu_bh_schedule(pool->completion_bh);
+        qemu_mutex_lock(&pool->lock);
     }
 
     pool->cur_threads--;
-- 
2.41.0.windows.1