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Will Deacon writes: > On Sun, Dec 14, 2025 at 08:49:11PM -0800, Ankur Arora wrote: >> Extend __cmpwait_relaxed() to __cmpwait_relaxed_timeout() which takes >> an additional timeout value in ns. >> >> Lacking WFET, or with zero or negative value of timeout we fallback >> to WFE. >> >> Cc: Arnd Bergmann >> Cc: Catalin Marinas >> Cc: Will Deacon >> Cc: linux-arm-kernel@lists.infradead.org >> Signed-off-by: Ankur Arora >> --- >> arch/arm64/include/asm/barrier.h | 8 ++-- >> arch/arm64/include/asm/cmpxchg.h | 72 ++++++++++++++++++++++---------- >> 2 files changed, 55 insertions(+), 25 deletions(-) > > Sorry, just spotted something else on this... > >> diff --git a/arch/arm64/include/asm/barrier.h b/arch/arm64/include/asm/barrier.h >> index 6190e178db51..fbd71cd4ef4e 100644 >> --- a/arch/arm64/include/asm/barrier.h >> +++ b/arch/arm64/include/asm/barrier.h >> @@ -224,8 +224,8 @@ do { \ >> extern bool arch_timer_evtstrm_available(void); >> >> /* >> - * In the common case, cpu_poll_relax() sits waiting in __cmpwait_relaxed() >> - * for the ptr value to change. >> + * In the common case, cpu_poll_relax() sits waiting in __cmpwait_relaxed()/ >> + * __cmpwait_relaxed_timeout() for the ptr value to change. >> * >> * Since this period is reasonably long, choose SMP_TIMEOUT_POLL_COUNT >> * to be 1, so smp_cond_load_{relaxed,acquire}_timeout() does a >> @@ -234,7 +234,9 @@ extern bool arch_timer_evtstrm_available(void); >> #define SMP_TIMEOUT_POLL_COUNT 1 >> >> #define cpu_poll_relax(ptr, val, timeout_ns) do { \ >> - if (arch_timer_evtstrm_available()) \ >> + if (alternative_has_cap_unlikely(ARM64_HAS_WFXT)) \ >> + __cmpwait_relaxed_timeout(ptr, val, timeout_ns); \ >> + else if (arch_timer_evtstrm_available()) \ >> __cmpwait_relaxed(ptr, val); \ > > Don't you want to make sure that we have the event stream available for > __cmpwait_relaxed_timeout() too? Otherwise, a large timeout is going to > cause problems. Would that help though? If called from smp_cond_load_relaxed_timeout() then we would wake up and just call __cmpwait_relaxed_timeout() again. Or did you mean other future users of __cmpwait_relaxed_timeout()? Also I remember the event stream coming up earlier and there the intent was to disable it if WFET was available: https://lore.kernel.org/lkml/aJ3d2uoKtDop_gQO@arm.com/. -- ankur