diff options
| author |   Uros Bizjak <ubizjak@gmail.com> | 2022-08-25 16:56:03 +0200 |
|---|---|---|
| committer |   Andrew Morton <akpm@linux-foundation.org> | 2022-09-11 21:55:10 -0700 |
| commit | 9a15193e23b780d1da77e3db18698beb0637897d (patch) | |
| tree | 789af806d1dfa280b4c6ef05d8dd5038fe855b89 | |
| parent | task_work: use try_cmpxchg in task_work_add, task_work_cancel_match and task_work_run (diff) | |
| download | linux-dev-9a15193e23b780d1da77e3db18698beb0637897d.tar.xz linux-dev-9a15193e23b780d1da77e3db18698beb0637897d.zip | |
smpboot: use atomic_try_cmpxchg in cpu_wait_death and cpu_report_death
Use atomic_try_cmpxchg instead of atomic_cmpxchg (*ptr, old, new) == old
in cpu_wait_death and cpu_report_death. x86 CMPXCHG instruction returns
success in ZF flag, so this change saves a compare after cmpxchg (and
related move instruction in front of cmpxchg). Also, atomic_try_cmpxchg
implicitly assigns old *ptr value to "old" when cmpxchg fails, enabling
further code simplifications.
No functional change intended.
Link: https://lkml.kernel.org/r/20220825145603.5811-1-ubizjak@gmail.com
Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
| -rw-r--r-- | kernel/smpboot.c | 15 |
1 files changed, 8 insertions, 7 deletions
diff --git a/kernel/smpboot.c b/kernel/smpboot.c index b9f54544e749..2c7396da470c 100644 --- a/kernel/smpboot.c +++ b/kernel/smpboot.c @@ -433,7 +433,7 @@ bool cpu_wait_death(unsigned int cpu, int seconds) /* The outgoing CPU will normally get done quite quickly. */ if (atomic_read(&per_cpu(cpu_hotplug_state, cpu)) == CPU_DEAD) - goto update_state; + goto update_state_early; udelay(5); /* But if the outgoing CPU dawdles, wait increasingly long times. */ @@ -444,16 +444,17 @@ bool cpu_wait_death(unsigned int cpu, int seconds) break; sleep_jf = DIV_ROUND_UP(sleep_jf * 11, 10); } -update_state: +update_state_early: oldstate = atomic_read(&per_cpu(cpu_hotplug_state, cpu)); +update_state: if (oldstate == CPU_DEAD) { /* Outgoing CPU died normally, update state. */ smp_mb(); /* atomic_read() before update. */ atomic_set(&per_cpu(cpu_hotplug_state, cpu), CPU_POST_DEAD); } else { /* Outgoing CPU still hasn't died, set state accordingly. */ - if (atomic_cmpxchg(&per_cpu(cpu_hotplug_state, cpu), - oldstate, CPU_BROKEN) != oldstate) + if (!atomic_try_cmpxchg(&per_cpu(cpu_hotplug_state, cpu), + &oldstate, CPU_BROKEN)) goto update_state; ret = false; } @@ -475,14 +476,14 @@ bool cpu_report_death(void) int newstate; int cpu = smp_processor_id(); + oldstate = atomic_read(&per_cpu(cpu_hotplug_state, cpu)); do { - oldstate = atomic_read(&per_cpu(cpu_hotplug_state, cpu)); if (oldstate != CPU_BROKEN) newstate = CPU_DEAD; else newstate = CPU_DEAD_FROZEN; - } while (atomic_cmpxchg(&per_cpu(cpu_hotplug_state, cpu), - oldstate, newstate) != oldstate); + } while (!atomic_try_cmpxchg(&per_cpu(cpu_hotplug_state, cpu), + &oldstate, newstate)); return newstate == CPU_DEAD; } |