From: christoffer.dall@linaro.org (Christoffer Dall)
To: linux-arm-kernel@lists.infradead.org
Subject: [PATCH v2 1/2] ARM: KVM: Yield CPU when vcpu executes a WFE
Date: Tue, 15 Oct 2013 18:14:17 -0700 [thread overview]
Message-ID: <20131016011417.GA24837@cbox> (raw)
In-Reply-To: <1381253894-18114-2-git-send-email-marc.zyngier@arm.com>
On Tue, Oct 08, 2013 at 06:38:13PM +0100, Marc Zyngier wrote:
> 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.
>
Patch looks good, I can just apply it and add the other one I just send
as a reply if there are no objections.
Sorry for the long turn-around on this one.
-Christoffer
next prev parent reply other threads:[~2013-10-16 1:14 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-10-08 17:38 [PATCH v2 0/2] KVM: Yield CPU when vcpu executes a WFE Marc Zyngier
2013-10-08 17:38 ` [PATCH v2 1/2] ARM: " Marc Zyngier
2013-10-16 1:13 ` [PATCH] KVM: ARM: Update comments for kvm_handle_wfi Christoffer Dall
2013-10-16 4:19 ` Bhushan Bharat-R65777
2013-10-16 4:37 ` Christoffer Dall
2013-10-16 1:14 ` Christoffer Dall [this message]
2013-10-16 7:08 ` [PATCH v2 1/2] ARM: KVM: Yield CPU when vcpu executes a WFE Marc Zyngier
2013-10-16 16:55 ` Christoffer Dall
2013-10-08 17:38 ` [PATCH v2 2/2] arm64: " Marc Zyngier
2013-10-16 1:14 ` Christoffer Dall
2013-10-09 9:12 ` [PATCH v2 0/2] " Raghavendra K T
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