From 9e9d673b2c84719937db5d6ab1d8cbcd7d45e974 Mon Sep 17 00:00:00 2001 From: Uros Bizjak Date: Thu, 23 Nov 2023 21:34:23 +0100 Subject: x86/smp: Use atomic_try_cmpxchg in native_stop_other_cpus() 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 Signed-off-by: Ingo Molnar Link: https://lore.kernel.org/r/20231123203605.3474745-2-ubizjak@gmail.com --- arch/x86/kernel/smp.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) (limited to 'arch/x86/kernel/smp.c') diff --git a/arch/x86/kernel/smp.c b/arch/x86/kernel/smp.c index 65dd44e3fc1c..1bb79526c217 100644 --- a/arch/x86/kernel/smp.c +++ b/arch/x86/kernel/smp.c @@ -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 */ -- cgit v1.2.3