58d5ec8f8e
On an (even slightly) oversubscribed system, spinlocks are quickly becoming a bottleneck, as some vcpus are spinning, waiting for a lock to be released, while the vcpu holding the lock may not be running at all. This creates contention, and the observed slowdown is 40x for hackbench. No, this isn't a typo. The solution is to trap blocking WFEs and tell KVM that we're now spinning. This ensures that other vpus will get a scheduling boost, allowing the lock to be released more quickly. Also, using CONFIG_HAVE_KVM_CPU_RELAX_INTERCEPT slightly improves the performance when the VM is severely overcommited. Quick test to estimate the performance: hackbench 1 process 1000 2xA15 host (baseline): 1.843s 2xA15 guest w/o patch: 2.083s 4xA15 guest w/o patch: 80.212s 8xA15 guest w/o patch: Could not be bothered to find out 2xA15 guest w/ patch: 2.102s 4xA15 guest w/ patch: 3.205s 8xA15 guest w/ patch: 6.887s So we go from a 40x degradation to 1.5x in the 2x overcommit case, which is vaguely more acceptable. Signed-off-by: Marc Zyngier <marc.zyngier@arm.com> Signed-off-by: Christoffer Dall <christoffer.dall@linaro.org>
72 lines
1.8 KiB
Plaintext
72 lines
1.8 KiB
Plaintext
#
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# KVM configuration
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#
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source "virt/kvm/Kconfig"
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menuconfig VIRTUALIZATION
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bool "Virtualization"
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---help---
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Say Y here to get to see options for using your Linux host to run
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other operating systems inside virtual machines (guests).
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This option alone does not add any kernel code.
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If you say N, all options in this submenu will be skipped and
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disabled.
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if VIRTUALIZATION
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config KVM
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bool "Kernel-based Virtual Machine (KVM) support"
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select PREEMPT_NOTIFIERS
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select ANON_INODES
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select HAVE_KVM_CPU_RELAX_INTERCEPT
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select KVM_MMIO
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select KVM_ARM_HOST
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depends on ARM_VIRT_EXT && ARM_LPAE
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---help---
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Support hosting virtualized guest machines. You will also
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need to select one or more of the processor modules below.
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This module provides access to the hardware capabilities through
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a character device node named /dev/kvm.
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If unsure, say N.
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config KVM_ARM_HOST
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bool "KVM host support for ARM cpus."
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depends on KVM
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depends on MMU
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select MMU_NOTIFIER
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---help---
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Provides host support for ARM processors.
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config KVM_ARM_MAX_VCPUS
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int "Number maximum supported virtual CPUs per VM"
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depends on KVM_ARM_HOST
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default 4
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help
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Static number of max supported virtual CPUs per VM.
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If you choose a high number, the vcpu structures will be quite
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large, so only choose a reasonable number that you expect to
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actually use.
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config KVM_ARM_VGIC
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bool "KVM support for Virtual GIC"
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depends on KVM_ARM_HOST && OF
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select HAVE_KVM_IRQCHIP
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default y
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---help---
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Adds support for a hardware assisted, in-kernel GIC emulation.
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config KVM_ARM_TIMER
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bool "KVM support for Architected Timers"
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depends on KVM_ARM_VGIC && ARM_ARCH_TIMER
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select HAVE_KVM_IRQCHIP
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default y
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---help---
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Adds support for the Architected Timers in virtual machines
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endif # VIRTUALIZATION
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