[RFC,v4,67/71] cpus-common: release BQL earlier in run_on_cpu

Commit Message

Emilio Cota Oct. 25, 2018, 2:46 p.m. UTC

After completing the conversion to per-CPU locks, there is no need
to release the BQL after having called cpu_kick.

Signed-off-by: Emilio G. Cota <[e-mail]>
---
 cpus-common.c | 20 +++++---------------
 1 file changed, 5 insertions(+), 15 deletions(-)

Comments

Richard Henderson Oct. 26, 2018, 3:59 p.m. UTC | #1

On 10/25/18 3:46 PM, Emilio G. Cota wrote:
> After completing the conversion to per-CPU locks, there is no need
> to release the BQL after having called cpu_kick.
> 
> Signed-off-by: Emilio G. Cota <[e-mail]>
> ---
>  cpus-common.c | 20 +++++---------------
>  1 file changed, 5 insertions(+), 15 deletions(-)

Reviewed-by: Richard Henderson <[e-mail]>

r~

Patch

diff --git a/cpus-common.c b/cpus-common.c
index c2ad554d54..80d7e300eb 100644
--- a/cpus-common.c
+++ b/cpus-common.c
@@ -145,6 +145,11 @@  void run_on_cpu(CPUState *cpu, run_on_cpu_func func, run_on_cpu_data data)
         return;
     }
 
+    /* We are going to sleep on the CPU lock, so release the BQL */
+    if (has_bql) {
+        qemu_mutex_unlock_iothread();
+    }
+
     wi.func = func;
     wi.data = data;
     wi.done = false;
@@ -153,21 +158,6 @@  void run_on_cpu(CPUState *cpu, run_on_cpu_func func, run_on_cpu_data data)
 
     cpu_mutex_lock(cpu);
     queue_work_on_cpu_locked(cpu, &wi);
-
-    /*
-     * We are going to sleep on the CPU lock, so release the BQL.
-     *
-     * During the transition to per-CPU locks, we release the BQL _after_
-     * having kicked the destination CPU (from queue_work_on_cpu_locked above).
-     * This makes sure that the enqueued work will be seen by the CPU
-     * after being woken up from the kick, since the CPU sleeps on the BQL.
-     * Once we complete the transition to per-CPU locks, we will release
-     * the BQL earlier in this function.
-     */
-    if (has_bql) {
-        qemu_mutex_unlock_iothread();
-    }
-
     while (!atomic_mb_read(&wi.done)) {
         CPUState *self_cpu = current_cpu;