Commit b8e3dfa1 authored by Uros Bizjak's avatar Uros Bizjak Committed by Ingo Molnar
Browse files

x86/percpu: Use raw_cpu_try_cmpxchg() in preempt_count_set() 



Use raw_cpu_try_cmpxchg() instead of raw_cpu_cmpxchg(*ptr, old, new) == old.
x86 CMPXCHG instruction returns success in ZF flag, so this change saves a
compare after CMPXCHG (and related MOV instruction in front of CMPXCHG).

Also, raw_cpu_try_cmpxchg() implicitly assigns old *ptr value to "old" when
cmpxchg fails. There is no need to re-read the value in the loop.

No functional change intended.

Signed-off-by: default avatarUros Bizjak <ubizjak@gmail.com>
Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lore.kernel.org/r/20230830151623.3900-2-ubizjak@gmail.com
parent 5f863897

arch/x86/include/asm/preempt.h

+2 −2
Original line number Diff line number Diff line
@@ -31,11 +31,11 @@ static __always_inline void preempt_count_set(int pc) 
{

	int old, new;



	do {

	old = raw_cpu_read_4(pcpu_hot.preempt_count);

	do {

		new = (old & PREEMPT_NEED_RESCHED) |

			(pc & ~PREEMPT_NEED_RESCHED);

	} while (raw_cpu_cmpxchg_4(pcpu_hot.preempt_count, old, new) != old);

	} while (!raw_cpu_try_cmpxchg_4(pcpu_hot.preempt_count, &old, new));

}



/*