diff options
| author | Uros Bizjak <ubizjak@gmail.com> | 2023-11-14 17:59:28 +0100 |
|---|---|---|
| committer | Wei Liu <wei.liu@kernel.org> | 2023-11-22 03:47:44 +0000 |
| commit | 18286883e779fb79b413a7462968ee3f6768f19c (patch) | |
| tree | 12ea006d25a8ad18ff1eb8e31788f7679c707324 /arch | |
| parent | 7e8037b099c0bbe8f2109dc452dbcab8d400fc53 (diff) | |
x86/hyperv: Use atomic_try_cmpxchg() to micro-optimize hv_nmi_unknown()
Use atomic_try_cmpxchg() instead of atomic_cmpxchg(*ptr, old, new) == old
in hv_nmi_unknown(). On x86 the CMPXCHG instruction returns success in
the ZF flag, so this change saves a compare after CMPXCHG. The generated
asm code improves from:
3e: 65 8b 15 00 00 00 00 mov %gs:0x0(%rip),%edx
45: b8 ff ff ff ff mov $0xffffffff,%eax
4a: f0 0f b1 15 00 00 00 lock cmpxchg %edx,0x0(%rip)
51: 00
52: 83 f8 ff cmp $0xffffffff,%eax
55: 0f 95 c0 setne %al
to:
3e: 65 8b 15 00 00 00 00 mov %gs:0x0(%rip),%edx
45: b8 ff ff ff ff mov $0xffffffff,%eax
4a: f0 0f b1 15 00 00 00 lock cmpxchg %edx,0x0(%rip)
51: 00
52: 0f 95 c0 setne %al
No functional change intended.
Cc: "K. Y. Srinivasan" <kys@microsoft.com>
Cc: Haiyang Zhang <haiyangz@microsoft.com>
Cc: Wei Liu <wei.liu@kernel.org>
Cc: Dexuan Cui <decui@microsoft.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Reviewed-by: Michael Kelley <mhklinux@outlook.com>
Link: https://lore.kernel.org/r/20231114170038.381634-1-ubizjak@gmail.com
Signed-off-by: Wei Liu <wei.liu@kernel.org>
Message-ID: <20231114170038.381634-1-ubizjak@gmail.com>
Diffstat (limited to 'arch')
| -rw-r--r-- | arch/x86/kernel/cpu/mshyperv.c | 5 |
1 files changed, 4 insertions, 1 deletions
diff --git a/arch/x86/kernel/cpu/mshyperv.c b/arch/x86/kernel/cpu/mshyperv.c index e6bba12c759c..01fa06dd06b6 100644 --- a/arch/x86/kernel/cpu/mshyperv.c +++ b/arch/x86/kernel/cpu/mshyperv.c @@ -262,11 +262,14 @@ static uint32_t __init ms_hyperv_platform(void) static int hv_nmi_unknown(unsigned int val, struct pt_regs *regs) { static atomic_t nmi_cpu = ATOMIC_INIT(-1); + unsigned int old_cpu, this_cpu; if (!unknown_nmi_panic) return NMI_DONE; - if (atomic_cmpxchg(&nmi_cpu, -1, raw_smp_processor_id()) != -1) + old_cpu = -1; + this_cpu = raw_smp_processor_id(); + if (!atomic_try_cmpxchg(&nmi_cpu, &old_cpu, this_cpu)) return NMI_HANDLED; return NMI_DONE; |