Use try_cmpxchg() instead of cmpxchg (*ptr, old, new) == old in
mm_cid_pcpu_unset(). x86 CMPXCHG instruction returns success in
ZF flag, so this change saves a compare after cmpxchg.
Also, try_cmpxchg() implicitly assigns old *ptr value to "old" when
cmpxchg fails, enabling substantial source code simplifications.
No functional change intended.
Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Vincent Guittot <vincent.guittot@linaro.org>
Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Ben Segall <bsegall@google.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Valentin Schneider <vschneid@redhat.com>
---
kernel/sched/sched.h | 15 +++++----------
1 file changed, 5 insertions(+), 10 deletions(-)
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 83e3aa917142..42006e8525c9 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -3647,21 +3647,16 @@ static inline void mm_cid_put_lazy(struct task_struct *t)
static inline int mm_cid_pcpu_unset(struct mm_struct *mm)
{
struct mm_cid __percpu *pcpu_cid = mm->pcpu_cid;
- int cid, res;
+ int cid;
lockdep_assert_irqs_disabled();
cid = __this_cpu_read(pcpu_cid->cid);
- for (;;) {
+ do {
if (mm_cid_is_unset(cid))
return MM_CID_UNSET;
- /*
- * Attempt transition from valid or lazy-put to unset.
- */
- res = cmpxchg(&this_cpu_ptr(pcpu_cid)->cid, cid, MM_CID_UNSET);
- if (res == cid)
- break;
- cid = res;
- }
+ /* Attempt transition from valid or lazy-put to unset. */
+ } while (!try_cmpxchg(&this_cpu_ptr(pcpu_cid)->cid, &cid, MM_CID_UNSET));
+
return cid;
}
--
2.50.1