diff options
| author | Uros Bizjak <ubizjak@gmail.com> | 2025-07-09 15:19:03 +0200 |
|---|---|---|
| committer | Tejun Heo <tj@kernel.org> | 2025-07-17 08:14:50 -1000 |
| commit | df316ab3d4440177e322a2847969d356c29b0eef (patch) | |
| tree | 60cfb4eec57bb2711388f605b6a481cf70c7c4f9 /kernel/workqueue.c | |
| parent | fc2898ea793a48bc4b74b61cde2d8656f20efdf4 (diff) | |
workqueue: Use atomic_try_cmpxchg_relaxed() in tryinc_node_nr_active()
Use try_cmpxchg() family of locking primitives instead of
cmpxchg(*ptr, old, new) == old.
The x86 CMPXCHG instruction returns success in the ZF flag, so this
change saves a compare after CMPXCHG (and related move instruction
in front of CMPXCHG).
Also, try_cmpxchg() implicitly assigns old *ptr value to "old" when
CMPXCHG fails. There is no need to re-read the value in the loop.
The generated assembly improves from:
3f7: 44 8b 0a mov (%rdx),%r9d
3fa: eb 12 jmp 40e <...>
3fc: 8d 79 01 lea 0x1(%rcx),%edi
3ff: 89 c8 mov %ecx,%eax
401: f0 0f b1 7a 04 lock cmpxchg %edi,0x4(%rdx)
406: 39 c1 cmp %eax,%ecx
408: 0f 84 83 00 00 00 je 491 <...>
40e: 8b 4a 04 mov 0x4(%rdx),%ecx
411: 41 39 c9 cmp %ecx,%r9d
414: 7f e6 jg 3fc <...>
to:
256b: 45 8b 08 mov (%r8),%r9d
256e: 41 8b 40 04 mov 0x4(%r8),%eax
2572: 41 39 c1 cmp %eax,%r9d
2575: 7e 10 jle 2587 <...>
2577: 8d 78 01 lea 0x1(%rax),%edi
257a: f0 41 0f b1 78 04 lock cmpxchg %edi,0x4(%r8)
2580: 75 f0 jne 2572 <...>
No functional change intended.
Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Lai Jiangshan <jiangshanlai@gmail.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
Diffstat (limited to 'kernel/workqueue.c')
| -rw-r--r-- | kernel/workqueue.c | 13 |
1 files changed, 5 insertions, 8 deletions
diff --git a/kernel/workqueue.c b/kernel/workqueue.c index 12c3080332bd..ad83662a0533 100644 --- a/kernel/workqueue.c +++ b/kernel/workqueue.c @@ -1690,17 +1690,14 @@ static void __pwq_activate_work(struct pool_workqueue *pwq, static bool tryinc_node_nr_active(struct wq_node_nr_active *nna) { int max = READ_ONCE(nna->max); + int old = atomic_read(&nna->nr); - while (true) { - int old, tmp; - - old = atomic_read(&nna->nr); + do { if (old >= max) return false; - tmp = atomic_cmpxchg_relaxed(&nna->nr, old, old + 1); - if (tmp == old) - return true; - } + } while (!atomic_try_cmpxchg_relaxed(&nna->nr, &old, old + 1)); + + return true; } /** |