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x86/smp: Use atomic_try_cmpxchg in native_stop_other_cpus()

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Use atomic_try_cmpxchg() instead of atomic_cmpxchg(*ptr, old, new) == old.

X86 CMPXCHG instruction returns success in ZF flag, so this change saves a
compare after the CMPXCHG.

Tested by building a native Fedora-38 kernel and rebooting
a 12-way SMP system using "shutdown -r" command some 100 times.

No functional change intended.

Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20231123203605.3474745-2-ubizjak@gmail.com
This commit is contained in:
Uros Bizjak 2023-11-23 21:34:23 +01:00 • committed by Ingo Molnar
parent 9d1c8f2153
commit 9e9d673b2c
1 changed files with 3 additions and 2 deletions
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5
arch/x86/kernel/smp.c
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@ -148,15 +148,16 @@ static int register_stop_handler(void)
static void native_stop_other_cpus(int wait)
{
unsigned int this_cpu;
unsigned int old_cpu, this_cpu;
unsigned long flags, timeout;
if (reboot_force)
return;
/* Only proceed if this is the first CPU to reach this code */
old_cpu = -1;
this_cpu = smp_processor_id();
if (atomic_cmpxchg(&stopping_cpu, -1, this_cpu) != -1)
if (!atomic_try_cmpxchg(&stopping_cpu, &old_cpu, this_cpu))
return;
/* For kexec, ensure that offline CPUs are out of MWAIT and in HLT */