[PULL 07/34] softmmu/cpus: Check if the cpu work list is empty atomically

[Richard Henderson <richard.henderson@linaro.org>]

From: Idan Horowitz <idan.horowitz@gmail.com>

Instead of taking the lock of the cpu work list in order to check if it's
empty, we can just read the head pointer atomically. This decreases
cpu_work_list_empty's share from 5% to 1.3% in a profile of icount-enabled
aarch64-softmmu.

Signed-off-by: Idan Horowitz <idan.horowitz@gmail.com>
Message-Id: <20220114004358.299534-1-idan.horowitz@gmail.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
---
 softmmu/cpus.c | 7 +------
 1 file changed, 1 insertion(+), 6 deletions(-)

diff --git a/softmmu/cpus.c b/softmmu/cpus.c
index 23bca46b07..035395ae13 100644
--- a/softmmu/cpus.c
+++ b/softmmu/cpus.c
@@ -73,12 +73,7 @@ bool cpu_is_stopped(CPUState *cpu)
 
 bool cpu_work_list_empty(CPUState *cpu)
 {
-    bool ret;
-
-    qemu_mutex_lock(&cpu->work_mutex);
-    ret = QSIMPLEQ_EMPTY(&cpu->work_list);
-    qemu_mutex_unlock(&cpu->work_mutex);
-    return ret;
+    return QSIMPLEQ_EMPTY_ATOMIC(&cpu->work_list);
 }
 
 bool cpu_thread_is_idle(CPUState *cpu)
-- 
2.25.1