Commit 7d26b051 authored by Marc Zyngier's avatar Marc Zyngier
Browse files

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: default avatarMarc Zyngier <maz@kernel.org>
Acked-by: default avatarCatalin Marinas <catalin.marinas@arm.com>
Link: https://lore.kernel.org/r/20220419182755.601427-11-maz@kernel.org
parent 9eae5885

arch/arm64/lib/delay.c

+11 −1
Original line number Diff line number Diff line
@@ -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);