Re: [PATCH v8 04/12] arm64: support WFET in smp_cond_relaxed_timeout()
From: Will Deacon <will@kernel.org>
Date: 2026-01-08 21:35:53
Also in:
bpf, linux-arch, linux-pm, lkml
On Sun, Dec 14, 2025 at 08:49:11PM -0800, Ankur Arora wrote:
+#define __CMPWAIT_CASE(w, sfx, sz) \
+static inline void __cmpwait_case_##sz(volatile void *ptr, \
+ unsigned long val, \
+ s64 timeout_ns) \
+{ \
+ unsigned long tmp; \
+ \
+ if (!alternative_has_cap_unlikely(ARM64_HAS_WFXT) || timeout_ns <= 0) { \
+ asm volatile( \
+ " sevl\n" \
+ " wfe\n" \
+ " ldxr" #sfx "\t%" #w "[tmp], %[v]\n" \
+ " eor %" #w "[tmp], %" #w "[tmp], %" #w "[val]\n" \
+ " cbnz %" #w "[tmp], 1f\n" \
+ " wfe\n" \
+ "1:" \
+ : [tmp] "=&r" (tmp), [v] "+Q" (*(u##sz *)ptr) \
+ : [val] "r" (val)); \
+ } else { \
+ u64 ecycles = arch_timer_read_counter() + \
+ NSECS_TO_CYCLES(timeout_ns); \
+ asm volatile( \
+ " sevl\n" \
+ " wfe\n" \
+ " ldxr" #sfx "\t%" #w "[tmp], %[v]\n" \
+ " eor %" #w "[tmp], %" #w "[tmp], %" #w "[val]\n" \
+ " cbnz %" #w "[tmp], 2f\n" \
+ " msr s0_3_c1_c0_0, %[ecycles]\n" \
+ "2:" \
+ : [tmp] "=&r" (tmp), [v] "+Q" (*(u##sz *)ptr) \
+ : [val] "r" (val), [ecycles] "r" (ecycles)); \
+ } \Why not have a separate helper for the WFXT version and avoid the runtime check on timeout_ns? Will