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arm64: Use WFxT for __delay() when possible

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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 <maz@kernel.org>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Link: https://lore.kernel.org/r/20220419182755.601427-11-maz@kernel.org
This commit is contained in:
Marc Zyngier 2022-04-19 19:27:55 +01:00
parent 9eae588529
commit 7d26b0516a
1 changed files with 11 additions and 1 deletions
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12
arch/arm64/lib/delay.c
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@ -27,7 +27,17 @@ void __delay(unsigned long cycles)
{ {
cycles_t start = get_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 = const cycles_t timer_evt_period =
USECS_TO_CYCLES(ARCH_TIMER_EVT_STREAM_PERIOD_US); USECS_TO_CYCLES(ARCH_TIMER_EVT_STREAM_PERIOD_US);