The following commit has been merged into the x86/percpu branch of tip:
Commit-ID: 9e9d673b2c84719937db5d6ab1d8cbcd7d45e974
Gitweb: https://git.kernel.org/tip/9e9d673b2c84719937db5d6ab1d8cbcd7d45e974
Author: Uros Bizjak <ubizjak@xxxxxxxxx>
AuthorDate: Thu, 23 Nov 2023 21:34:23 +01:00
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
CommitterDate: Thu, 30 Nov 2023 20:25:09 +01:00
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 <ubizjak@xxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20231123203605.3474745-2-ubizjak@xxxxxxxxx
---
arch/x86/kernel/smp.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)
diff --git a/arch/x86/kernel/smp.c b/arch/x86/kernel/smp.c
index 65dd44e..1bb7952 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 */
|