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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 <[email protected]>
Acked-by: Catalin Marinas <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
This commit is contained in:
Marc Zyngier committed 2022-04-20 13:24:44 +01:00
1 parent 9eae588529
commit 7d26b0516a
1 file changed
+11 -1
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arch/arm64/lib/delay.c
+11 -1
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@@ -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);