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From: Christoffer Dall <cdall@linaro.org>
To: kvmarm@lists.cs.columbia.edu, linux-arm-kernel@lists.infradead.org
Cc: kvm@vger.kernel.org, Marc Zyngier <marc.zyngier@arm.com>,
	Will Deacon <will.deacon@arm.com>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Christoffer Dall <cdall@linaro.org>
Subject: [PATCH v3 02/20] arm64: Use physical counter for in-kernel reads
Date: Sat, 23 Sep 2017 02:41:49 +0200	[thread overview]
Message-ID: <20170923004207.22356-3-cdall@linaro.org> (raw)
In-Reply-To: <20170923004207.22356-1-cdall@linaro.org>

Using the physical counter allows KVM to retain the offset between the
virtual and physical counter as long as it is actively running a VCPU.

As soon as a VCPU is released, another thread is scheduled or we start
running userspace applications, we reset the offset to 0, so that
userspace accessing the virtual timer can still read the cirtual counter
and get the same view of time as the kernel.

This opens up potential improvements for KVM performance.

VHE kernels or kernels continuing to use the virtual timer are
unaffected.

Signed-off-by: Christoffer Dall <cdall@linaro.org>
---
 arch/arm64/include/asm/arch_timer.h  | 9 ++++-----
 drivers/clocksource/arm_arch_timer.c | 3 +--
 2 files changed, 5 insertions(+), 7 deletions(-)

diff --git a/arch/arm64/include/asm/arch_timer.h b/arch/arm64/include/asm/arch_timer.h
index a652ce0..1859a1c 100644
--- a/arch/arm64/include/asm/arch_timer.h
+++ b/arch/arm64/include/asm/arch_timer.h
@@ -148,11 +148,10 @@ static inline void arch_timer_set_cntkctl(u32 cntkctl)
 
 static inline u64 arch_counter_get_cntpct(void)
 {
-	/*
-	 * AArch64 kernel and user space mandate the use of CNTVCT.
-	 */
-	BUG();
-	return 0;
+	u64 cval;
+	isb();
+	asm volatile("mrs %0, cntpct_el0" : "=r" (cval));
+	return cval;
 }
 
 static inline u64 arch_counter_get_cntvct(void)
diff --git a/drivers/clocksource/arm_arch_timer.c b/drivers/clocksource/arm_arch_timer.c
index fd4b7f6..9b3322a 100644
--- a/drivers/clocksource/arm_arch_timer.c
+++ b/drivers/clocksource/arm_arch_timer.c
@@ -890,8 +890,7 @@ static void __init arch_counter_register(unsigned type)
 
 	/* Register the CP15 based counter if we have one */
 	if (type & ARCH_TIMER_TYPE_CP15) {
-		if (IS_ENABLED(CONFIG_ARM64) ||
-		    arch_timer_uses_ppi == ARCH_TIMER_VIRT_PPI)
+		if (arch_timer_uses_ppi == ARCH_TIMER_VIRT_PPI)
 			arch_timer_read_counter = arch_counter_get_cntvct;
 		else
 			arch_timer_read_counter = arch_counter_get_cntpct;
-- 
2.9.0

WARNING: multiple messages have this Message-ID (diff)
From: cdall@linaro.org (Christoffer Dall)
To: linux-arm-kernel@lists.infradead.org
Subject: [PATCH v3 02/20] arm64: Use physical counter for in-kernel reads
Date: Sat, 23 Sep 2017 02:41:49 +0200	[thread overview]
Message-ID: <20170923004207.22356-3-cdall@linaro.org> (raw)
In-Reply-To: <20170923004207.22356-1-cdall@linaro.org>

Using the physical counter allows KVM to retain the offset between the
virtual and physical counter as long as it is actively running a VCPU.

As soon as a VCPU is released, another thread is scheduled or we start
running userspace applications, we reset the offset to 0, so that
userspace accessing the virtual timer can still read the cirtual counter
and get the same view of time as the kernel.

This opens up potential improvements for KVM performance.

VHE kernels or kernels continuing to use the virtual timer are
unaffected.

Signed-off-by: Christoffer Dall <cdall@linaro.org>
---
 arch/arm64/include/asm/arch_timer.h  | 9 ++++-----
 drivers/clocksource/arm_arch_timer.c | 3 +--
 2 files changed, 5 insertions(+), 7 deletions(-)

diff --git a/arch/arm64/include/asm/arch_timer.h b/arch/arm64/include/asm/arch_timer.h
index a652ce0..1859a1c 100644
--- a/arch/arm64/include/asm/arch_timer.h
+++ b/arch/arm64/include/asm/arch_timer.h
@@ -148,11 +148,10 @@ static inline void arch_timer_set_cntkctl(u32 cntkctl)
 
 static inline u64 arch_counter_get_cntpct(void)
 {
-	/*
-	 * AArch64 kernel and user space mandate the use of CNTVCT.
-	 */
-	BUG();
-	return 0;
+	u64 cval;
+	isb();
+	asm volatile("mrs %0, cntpct_el0" : "=r" (cval));
+	return cval;
 }
 
 static inline u64 arch_counter_get_cntvct(void)
diff --git a/drivers/clocksource/arm_arch_timer.c b/drivers/clocksource/arm_arch_timer.c
index fd4b7f6..9b3322a 100644
--- a/drivers/clocksource/arm_arch_timer.c
+++ b/drivers/clocksource/arm_arch_timer.c
@@ -890,8 +890,7 @@ static void __init arch_counter_register(unsigned type)
 
 	/* Register the CP15 based counter if we have one */
 	if (type & ARCH_TIMER_TYPE_CP15) {
-		if (IS_ENABLED(CONFIG_ARM64) ||
-		    arch_timer_uses_ppi == ARCH_TIMER_VIRT_PPI)
+		if (arch_timer_uses_ppi == ARCH_TIMER_VIRT_PPI)
 			arch_timer_read_counter = arch_counter_get_cntvct;
 		else
 			arch_timer_read_counter = arch_counter_get_cntpct;
-- 
2.9.0

  parent reply	other threads:[~2017-09-23  0:42 UTC|newest]

Thread overview: 110+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-09-23  0:41 [PATCH v3 00/20] KVM: arm/arm64: Optimize arch timer register handling Christoffer Dall
2017-09-23  0:41 ` Christoffer Dall
2017-09-23  0:41 ` [PATCH v3 01/20] irqchip/gic: Deal with broken firmware exposing only 4kB of GICv2 CPU interface Christoffer Dall
2017-09-23  0:41   ` Christoffer Dall
2017-09-23  0:41 ` Christoffer Dall [this message]
2017-09-23  0:41   ` [PATCH v3 02/20] arm64: Use physical counter for in-kernel reads Christoffer Dall
2017-10-09 16:10   ` Marc Zyngier
2017-10-09 16:10     ` Marc Zyngier
2017-10-17 15:33   ` Will Deacon
2017-10-17 15:33     ` Will Deacon
2017-10-18 10:00     ` Christoffer Dall
2017-10-18 10:00       ` Christoffer Dall
2017-09-23  0:41 ` [PATCH v3 03/20] arm64: Use the physical counter when available for read_cycles Christoffer Dall
2017-09-23  0:41   ` Christoffer Dall
2017-10-09 16:21   ` Marc Zyngier
2017-10-09 16:21     ` Marc Zyngier
2017-10-18 11:34     ` Christoffer Dall
2017-10-18 11:34       ` Christoffer Dall
2017-10-18 15:52       ` Marc Zyngier
2017-10-18 15:52         ` Marc Zyngier
2017-09-23  0:41 ` [PATCH v3 04/20] KVM: arm/arm64: Guard kvm_vgic_map_is_active against !vgic_initialized Christoffer Dall
2017-09-23  0:41   ` Christoffer Dall
2017-10-09 16:22   ` Marc Zyngier
2017-10-09 16:22     ` Marc Zyngier
2017-09-23  0:41 ` [PATCH v3 05/20] KVM: arm/arm64: Support calling vgic_update_irq_pending from irq context Christoffer Dall
2017-09-23  0:41   ` Christoffer Dall
2017-10-09 16:37   ` Marc Zyngier
2017-10-09 16:37     ` Marc Zyngier
2017-10-18 11:54     ` Christoffer Dall
2017-10-18 11:54       ` Christoffer Dall
2017-09-23  0:41 ` [PATCH v3 06/20] KVM: arm/arm64: Check that system supports split eoi/deactivate Christoffer Dall
2017-09-23  0:41   ` Christoffer Dall
2017-10-09 16:47   ` Marc Zyngier
2017-10-09 16:47     ` Marc Zyngier
2017-10-18 13:41     ` Christoffer Dall
2017-10-18 13:41       ` Christoffer Dall
2017-10-18 16:03       ` Marc Zyngier
2017-10-18 16:03         ` Marc Zyngier
2017-10-18 19:16         ` Christoffer Dall
2017-10-18 19:16           ` Christoffer Dall
2017-09-23  0:41 ` [PATCH v3 07/20] KVM: arm/arm64: Make timer_arm and timer_disarm helpers more generic Christoffer Dall
2017-09-23  0:41   ` Christoffer Dall
2017-10-09 17:05   ` Marc Zyngier
2017-10-09 17:05     ` Marc Zyngier
2017-10-18 16:47     ` Christoffer Dall
2017-10-18 16:47       ` Christoffer Dall
2017-10-18 16:53       ` Marc Zyngier
2017-10-18 16:53         ` Marc Zyngier
2017-09-23  0:41 ` [PATCH v3 08/20] KVM: arm/arm64: Rename soft timer to bg_timer Christoffer Dall
2017-09-23  0:41   ` Christoffer Dall
2017-10-09 17:06   ` Marc Zyngier
2017-10-09 17:06     ` Marc Zyngier
2017-09-23  0:41 ` [PATCH v3 09/20] KVM: arm/arm64: Use separate timer for phys timer emulation Christoffer Dall
2017-09-23  0:41   ` Christoffer Dall
2017-10-09 17:23   ` Marc Zyngier
2017-10-09 17:23     ` Marc Zyngier
2017-10-19  7:38     ` Christoffer Dall
2017-10-19  7:38       ` Christoffer Dall
2017-09-23  0:41 ` [PATCH v3 10/20] KVM: arm/arm64: Move timer/vgic flush/sync under disabled irq Christoffer Dall
2017-09-23  0:41   ` Christoffer Dall
2017-10-09 17:34   ` Marc Zyngier
2017-10-09 17:34     ` Marc Zyngier
2017-09-23  0:41 ` [PATCH v3 11/20] KVM: arm/arm64: Move timer save/restore out of the hyp code Christoffer Dall
2017-09-23  0:41   ` Christoffer Dall
2017-10-09 17:47   ` Marc Zyngier
2017-10-09 17:47     ` Marc Zyngier
2017-10-19  7:46     ` Christoffer Dall
2017-10-19  7:46       ` Christoffer Dall
2017-09-23  0:41 ` [PATCH v3 12/20] genirq: Document vcpu_info usage for percpu_devid interrupts Christoffer Dall
2017-09-23  0:41   ` Christoffer Dall
2017-10-09 17:48   ` Marc Zyngier
2017-10-09 17:48     ` Marc Zyngier
2017-09-23  0:42 ` [PATCH v3 13/20] KVM: arm/arm64: Set VCPU affinity for virt timer irq Christoffer Dall
2017-09-23  0:42   ` Christoffer Dall
2017-10-09 17:52   ` Marc Zyngier
2017-10-09 17:52     ` Marc Zyngier
2017-09-23  0:42 ` [PATCH v3 14/20] KVM: arm/arm64: Avoid timer save/restore in vcpu entry/exit Christoffer Dall
2017-09-23  0:42   ` Christoffer Dall
2017-10-10  8:47   ` Marc Zyngier
2017-10-10  8:47     ` Marc Zyngier
2017-10-19  8:15     ` Christoffer Dall
2017-10-19  8:15       ` Christoffer Dall
2017-09-23  0:42 ` [PATCH v3 15/20] KVM: arm/arm64: Support EL1 phys timer register access in set/get reg Christoffer Dall
2017-09-23  0:42   ` Christoffer Dall
2017-10-10  9:10   ` Marc Zyngier
2017-10-10  9:10     ` Marc Zyngier
2017-10-19  8:32     ` Christoffer Dall
2017-10-19  8:32       ` Christoffer Dall
2017-09-23  0:42 ` [PATCH v3 16/20] KVM: arm/arm64: Use kvm_arm_timer_set/get_reg for guest register traps Christoffer Dall
2017-09-23  0:42   ` Christoffer Dall
2017-10-10  9:12   ` Marc Zyngier
2017-10-10  9:12     ` Marc Zyngier
2017-09-23  0:42 ` [PATCH v3 17/20] KVM: arm/arm64: Move phys_timer_emulate function Christoffer Dall
2017-09-23  0:42   ` Christoffer Dall
2017-10-10  9:21   ` Marc Zyngier
2017-10-10  9:21     ` Marc Zyngier
2017-09-23  0:42 ` [PATCH v3 18/20] KVM: arm/arm64: Avoid phys timer emulation in vcpu entry/exit Christoffer Dall
2017-09-23  0:42   ` Christoffer Dall
2017-10-10  9:45   ` Marc Zyngier
2017-10-10  9:45     ` Marc Zyngier
2017-10-19  8:44     ` Christoffer Dall
2017-10-19  8:44       ` Christoffer Dall
2017-09-23  0:42 ` [PATCH v3 19/20] KVM: arm/arm64: Get rid of kvm_timer_flush_hwstate Christoffer Dall
2017-09-23  0:42   ` Christoffer Dall
2017-10-10  9:46   ` Marc Zyngier
2017-10-10  9:46     ` Marc Zyngier
2017-09-23  0:42 ` [PATCH v3 20/20] KVM: arm/arm64: Rework kvm_timer_should_fire Christoffer Dall
2017-09-23  0:42   ` Christoffer Dall
2017-10-10  9:59   ` Marc Zyngier
2017-10-10  9:59     ` Marc Zyngier

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