From 7d26b0516a0df5888fd1486054bc5159f6c0b88f Mon Sep 17 00:00:00 2001 From: Marc Zyngier Date: Tue, 19 Apr 2022 19:27:55 +0100 Subject: [PATCH] arm64: Use WFxT for __delay() when possible Marginally optimise __delay() by using a WFIT/WFET sequence. It probably is a win if no interrupt fires during the delay. Signed-off-by: Marc Zyngier Acked-by: Catalin Marinas Link: https://lore.kernel.org/r/20220419182755.601427-11-maz@kernel.org --- arch/arm64/lib/delay.c | 12 +++++++++++- 1 file changed, 11 insertions(+), 1 deletion(-) diff --git a/arch/arm64/lib/delay.c b/arch/arm64/lib/delay.c index 1688af0a4c97..5b7890139bc2 100644 --- a/arch/arm64/lib/delay.c +++ b/arch/arm64/lib/delay.c @@ -27,7 +27,17 @@ void __delay(unsigned long cycles) { cycles_t start = get_cycles(); - if (arch_timer_evtstrm_available()) { + if (cpus_have_const_cap(ARM64_HAS_WFXT)) { + u64 end = start + cycles; + + /* + * Start with WFIT. If an interrupt makes us resume + * early, use a WFET loop to complete the delay. + */ + wfit(end); + while ((get_cycles() - start) < cycles) + wfet(end); + } else if (arch_timer_evtstrm_available()) { const cycles_t timer_evt_period = USECS_TO_CYCLES(ARCH_TIMER_EVT_STREAM_PERIOD_US);