From mboxrd@z Thu Jan 1 00:00:00 1970 From: Christoffer Dall Subject: [PATCH v3 00/20] KVM: arm/arm64: Optimize arch timer register handling Date: Sat, 23 Sep 2017 02:41:47 +0200 Message-ID: <20170923004207.22356-1-cdall@linaro.org> Cc: kvm@vger.kernel.org, Marc Zyngier , Will Deacon , Catalin Marinas , Christoffer Dall To: kvmarm@lists.cs.columbia.edu, linux-arm-kernel@lists.infradead.org Return-path: Received: from mail-wm0-f51.google.com ([74.125.82.51]:46492 "EHLO mail-wm0-f51.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752004AbdIWAmE (ORCPT ); Fri, 22 Sep 2017 20:42:04 -0400 Received: by mail-wm0-f51.google.com with SMTP id m72so7631009wmc.1 for ; Fri, 22 Sep 2017 17:42:03 -0700 (PDT) Sender: kvm-owner@vger.kernel.org List-ID: We currently spend a measurable amount of time on each entry/exit to the guest dealing with arch timer registers, even when the timer is not pending and not doing anything (on certain architectures). We can do much better by moving the arch timer save/restore to the vcpu_load and vcpu_put functions, but this means that if we don't read back the timer state on every exit from the guest, then we have to be able to start taking timer interrupts for the virtual timer in KVM and handle that properly. That has a number of entertaining consequences, such as having to make sure we don't deadlock between any of the vgic code and interrupt injection happening from an ISR. On the plus side, being able to inject virtual interrupts corresponding to a physical interrupt directly from an ISR is probably a good system design change overall. We also have to change the use of the physical vs. virtual counter in the arm64 kernel to avoid having to save/restore the CNTVOFF_EL2 register on every return to the hypervisor. The only reason I could find for using the virtual counter for the kernel on systems with access to the physical counter is to detect if firmware did not properly clear CNTVOFF_EL2, and this change has to weighed against the existing check (assuming I got this right). On a non-VHE system (AMD Seattle) I have measured this to improve the world-switch time by about ~100 cycles, but on an EL2 kernel (emulating VHE behavior on the same hardware) this gives us around ~250 cycles worth of improvement, and on Thunder-X we seem to get ~650 cycles improvement, because we can avoid the extra configuration of trapping accesses to the physical timer from EL1 on every switch. These patches require that the GICv2 hardware (on such systems) is properly reported by firmware to have the extra CPU interface page for the deactivate register. Code is also available here: git://git.kernel.org/pub/scm/linux/kernel/git/cdall/linux.git timer-optimize-v3 Based on v4.14-rc1 Some recent numbers I ran on Thunder-X with v4.14-rc1 with/without these patches (averaged over a few hundred thousand executions) for a base hypercall cost: Without this series, avg. cycles: 12,476 Without this series, min. cycles: 12,052 With this series, avg. cycles: 11,782 With this series, min. cycles: 11,435 Improvement ~650 cycles (over 5%) Changes since v2: - Removed RFC tag - Included Marc's patch to support EOI/deactivate on broken firmware systems - Simplified patch 6 (was patch 5 in RFC v2) - Clarify percpu_devid interrupts in patch 12 (was patch 11) Thanks, Christoffer Christoffer Dall (19): arm64: Use physical counter for in-kernel reads arm64: Use the physical counter when available for read_cycles KVM: arm/arm64: Guard kvm_vgic_map_is_active against !vgic_initialized KVM: arm/arm64: Support calling vgic_update_irq_pending from irq context KVM: arm/arm64: Check that system supports split eoi/deactivate KVM: arm/arm64: Make timer_arm and timer_disarm helpers more generic KVM: arm/arm64: Rename soft timer to bg_timer KVM: arm/arm64: Use separate timer for phys timer emulation KVM: arm/arm64: Move timer/vgic flush/sync under disabled irq KVM: arm/arm64: Move timer save/restore out of the hyp code genirq: Document vcpu_info usage for percpu_devid interrupts KVM: arm/arm64: Set VCPU affinity for virt timer irq KVM: arm/arm64: Avoid timer save/restore in vcpu entry/exit KVM: arm/arm64: Support EL1 phys timer register access in set/get reg KVM: arm/arm64: Use kvm_arm_timer_set/get_reg for guest register traps KVM: arm/arm64: Move phys_timer_emulate function KVM: arm/arm64: Avoid phys timer emulation in vcpu entry/exit KVM: arm/arm64: Get rid of kvm_timer_flush_hwstate KVM: arm/arm64: Rework kvm_timer_should_fire Marc Zyngier (1): irqchip/gic: Deal with broken firmware exposing only 4kB of GICv2 CPU interface Documentation/admin-guide/kernel-parameters.txt | 7 + arch/arm/include/asm/kvm_asm.h | 2 + arch/arm/include/asm/kvm_hyp.h | 4 +- arch/arm/include/uapi/asm/kvm.h | 6 + arch/arm/kvm/hyp/switch.c | 7 +- arch/arm64/include/asm/arch_timer.h | 18 +- arch/arm64/include/asm/kvm_asm.h | 2 + arch/arm64/include/asm/kvm_hyp.h | 4 +- arch/arm64/include/asm/timex.h | 2 +- arch/arm64/include/uapi/asm/kvm.h | 6 + arch/arm64/kvm/hyp/switch.c | 6 +- arch/arm64/kvm/sys_regs.c | 41 +-- drivers/clocksource/arm_arch_timer.c | 33 +- drivers/irqchip/irq-gic.c | 74 +++- include/kvm/arm_arch_timer.h | 19 +- kernel/irq/manage.c | 3 +- virt/kvm/arm/arch_timer.c | 446 ++++++++++++++++-------- virt/kvm/arm/arm.c | 45 ++- virt/kvm/arm/hyp/timer-sr.c | 74 ++-- virt/kvm/arm/vgic/vgic-its.c | 17 +- virt/kvm/arm/vgic/vgic-mmio-v2.c | 22 +- virt/kvm/arm/vgic/vgic-mmio-v3.c | 17 +- virt/kvm/arm/vgic/vgic-mmio.c | 44 ++- virt/kvm/arm/vgic/vgic-v2.c | 5 +- virt/kvm/arm/vgic/vgic-v3.c | 12 +- virt/kvm/arm/vgic/vgic.c | 63 ++-- virt/kvm/arm/vgic/vgic.h | 3 +- 27 files changed, 648 insertions(+), 334 deletions(-) -- 2.9.0 From mboxrd@z Thu Jan 1 00:00:00 1970 From: cdall@linaro.org (Christoffer Dall) Date: Sat, 23 Sep 2017 02:41:47 +0200 Subject: [PATCH v3 00/20] KVM: arm/arm64: Optimize arch timer register handling Message-ID: <20170923004207.22356-1-cdall@linaro.org> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org We currently spend a measurable amount of time on each entry/exit to the guest dealing with arch timer registers, even when the timer is not pending and not doing anything (on certain architectures). We can do much better by moving the arch timer save/restore to the vcpu_load and vcpu_put functions, but this means that if we don't read back the timer state on every exit from the guest, then we have to be able to start taking timer interrupts for the virtual timer in KVM and handle that properly. That has a number of entertaining consequences, such as having to make sure we don't deadlock between any of the vgic code and interrupt injection happening from an ISR. On the plus side, being able to inject virtual interrupts corresponding to a physical interrupt directly from an ISR is probably a good system design change overall. We also have to change the use of the physical vs. virtual counter in the arm64 kernel to avoid having to save/restore the CNTVOFF_EL2 register on every return to the hypervisor. The only reason I could find for using the virtual counter for the kernel on systems with access to the physical counter is to detect if firmware did not properly clear CNTVOFF_EL2, and this change has to weighed against the existing check (assuming I got this right). On a non-VHE system (AMD Seattle) I have measured this to improve the world-switch time by about ~100 cycles, but on an EL2 kernel (emulating VHE behavior on the same hardware) this gives us around ~250 cycles worth of improvement, and on Thunder-X we seem to get ~650 cycles improvement, because we can avoid the extra configuration of trapping accesses to the physical timer from EL1 on every switch. These patches require that the GICv2 hardware (on such systems) is properly reported by firmware to have the extra CPU interface page for the deactivate register. Code is also available here: git://git.kernel.org/pub/scm/linux/kernel/git/cdall/linux.git timer-optimize-v3 Based on v4.14-rc1 Some recent numbers I ran on Thunder-X with v4.14-rc1 with/without these patches (averaged over a few hundred thousand executions) for a base hypercall cost: Without this series, avg. cycles: 12,476 Without this series, min. cycles: 12,052 With this series, avg. cycles: 11,782 With this series, min. cycles: 11,435 Improvement ~650 cycles (over 5%) Changes since v2: - Removed RFC tag - Included Marc's patch to support EOI/deactivate on broken firmware systems - Simplified patch 6 (was patch 5 in RFC v2) - Clarify percpu_devid interrupts in patch 12 (was patch 11) Thanks, Christoffer Christoffer Dall (19): arm64: Use physical counter for in-kernel reads arm64: Use the physical counter when available for read_cycles KVM: arm/arm64: Guard kvm_vgic_map_is_active against !vgic_initialized KVM: arm/arm64: Support calling vgic_update_irq_pending from irq context KVM: arm/arm64: Check that system supports split eoi/deactivate KVM: arm/arm64: Make timer_arm and timer_disarm helpers more generic KVM: arm/arm64: Rename soft timer to bg_timer KVM: arm/arm64: Use separate timer for phys timer emulation KVM: arm/arm64: Move timer/vgic flush/sync under disabled irq KVM: arm/arm64: Move timer save/restore out of the hyp code genirq: Document vcpu_info usage for percpu_devid interrupts KVM: arm/arm64: Set VCPU affinity for virt timer irq KVM: arm/arm64: Avoid timer save/restore in vcpu entry/exit KVM: arm/arm64: Support EL1 phys timer register access in set/get reg KVM: arm/arm64: Use kvm_arm_timer_set/get_reg for guest register traps KVM: arm/arm64: Move phys_timer_emulate function KVM: arm/arm64: Avoid phys timer emulation in vcpu entry/exit KVM: arm/arm64: Get rid of kvm_timer_flush_hwstate KVM: arm/arm64: Rework kvm_timer_should_fire Marc Zyngier (1): irqchip/gic: Deal with broken firmware exposing only 4kB of GICv2 CPU interface Documentation/admin-guide/kernel-parameters.txt | 7 + arch/arm/include/asm/kvm_asm.h | 2 + arch/arm/include/asm/kvm_hyp.h | 4 +- arch/arm/include/uapi/asm/kvm.h | 6 + arch/arm/kvm/hyp/switch.c | 7 +- arch/arm64/include/asm/arch_timer.h | 18 +- arch/arm64/include/asm/kvm_asm.h | 2 + arch/arm64/include/asm/kvm_hyp.h | 4 +- arch/arm64/include/asm/timex.h | 2 +- arch/arm64/include/uapi/asm/kvm.h | 6 + arch/arm64/kvm/hyp/switch.c | 6 +- arch/arm64/kvm/sys_regs.c | 41 +-- drivers/clocksource/arm_arch_timer.c | 33 +- drivers/irqchip/irq-gic.c | 74 +++- include/kvm/arm_arch_timer.h | 19 +- kernel/irq/manage.c | 3 +- virt/kvm/arm/arch_timer.c | 446 ++++++++++++++++-------- virt/kvm/arm/arm.c | 45 ++- virt/kvm/arm/hyp/timer-sr.c | 74 ++-- virt/kvm/arm/vgic/vgic-its.c | 17 +- virt/kvm/arm/vgic/vgic-mmio-v2.c | 22 +- virt/kvm/arm/vgic/vgic-mmio-v3.c | 17 +- virt/kvm/arm/vgic/vgic-mmio.c | 44 ++- virt/kvm/arm/vgic/vgic-v2.c | 5 +- virt/kvm/arm/vgic/vgic-v3.c | 12 +- virt/kvm/arm/vgic/vgic.c | 63 ++-- virt/kvm/arm/vgic/vgic.h | 3 +- 27 files changed, 648 insertions(+), 334 deletions(-) -- 2.9.0