From: Marc Zyngier <maz@kernel.org>
To: linux-arm-kernel@lists.infradead.org,
kvmarm@lists.cs.columbia.edu, kvm@vger.kernel.org
Cc: Catalin Marinas <catalin.marinas@arm.com>,
Will Deacon <will@kernel.org>,
Mark Rutland <mark.rutland@arm.com>,
James Morse <james.morse@arm.com>,
Suzuki K Poulose <suzuki.poulose@arm.com>,
Alexandru Elisei <alexandru.elisei@arm.com>,
kernel-team@android.com
Subject: [PATCH 10/10] arm64: Use WFxT for __delay() when possible
Date: Tue, 12 Apr 2022 14:13:03 +0100 [thread overview]
Message-ID: <20220412131303.504690-11-maz@kernel.org> (raw)
In-Reply-To: <20220412131303.504690-1-maz@kernel.org>
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>
---
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);
--
2.34.1
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prev parent reply other threads:[~2022-04-12 13:22 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-04-12 13:12 [PATCH 00/10] arm64: Add initial support for FEAT_WFxT Marc Zyngier
2022-04-12 13:12 ` [PATCH 01/10] arm64: Expand ESR_ELx_WFx_ISS_TI to match its ARMv8.7 definition Marc Zyngier
2022-04-13 11:50 ` Joey Gouly
2022-04-12 13:12 ` [PATCH 02/10] arm64: Add RV and RN fields for ESR_ELx_WFx_ISS Marc Zyngier
2022-04-13 11:53 ` Joey Gouly
2022-04-12 13:12 ` [PATCH 03/10] KVM: arm64: Simplify kvm_cpu_has_pending_timer() Marc Zyngier
2022-04-12 13:12 ` [PATCH 04/10] KVM: arm64: Introduce kvm_counter_compute_delta() helper Marc Zyngier
2022-04-12 13:12 ` [PATCH 05/10] KVM: arm64: Handle blocking WFIT instruction Marc Zyngier
2022-04-12 13:12 ` [PATCH 06/10] KVM: arm64: Offer early resume for non-blocking WFxT instructions Marc Zyngier
2022-04-13 11:37 ` Joey Gouly
2022-04-13 13:46 ` Marc Zyngier
2022-04-12 13:13 ` [PATCH 07/10] KVM: arm64: Expose the WFXT feature to guests Marc Zyngier
2022-04-12 13:13 ` [PATCH 08/10] arm64: Add HWCAP advertising FEAT_WFXT Marc Zyngier
2022-04-12 13:13 ` [PATCH 09/10] arm64: Add wfet()/wfit() helpers Marc Zyngier
2022-04-12 13:13 ` Marc Zyngier [this message]
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