sched/clock: Use try_cmpxchg64 in sched_clock_{local,remote}

Use try_cmpxchg64 instead of cmpxchg64 (*ptr, old, new) != old in sched_clock_{local,remote}. x86 cmpxchg returns success in ZF flag, so this change saves a compare after cmpxchg (and related move instruction in front of cmpxchg).

Uros Bizjak committed 4 years ago

Commit 8491d1b1 parent c2df0a61 file · +2 −2Browse files

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kernel/sched/clock.c+2−2

@@ -287,7 +287,7 @@ again: · 286 unmodified lines
287	287	clock = wrap_max(clock, min_clock);
288	288	clock = wrap_min(clock, max_clock);
289	289
290		− if (cmpxchg64(&scd->clock, old_clock, clock) != old_clock)
	290	+ if (!try_cmpxchg64(&scd->clock, &old_clock, clock))
291	291	goto again;
292	292
293	293	return clock;
@@ -349,7 +349,7 @@ again: · 55 unmodified lines
349	349	val = remote_clock;
350	350	}
351	351
352		− if (cmpxchg64(ptr, old_val, val) != old_val)
	352	+ if (!try_cmpxchg64(ptr, &old_val, val))
353	353	goto again;
354	354
355	355	return val;