linux-kernel - Re: [PATCH] sched,kvm: Fix KVM preempt

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Message-ID: <20150703121907.GH19282@twins.programming.kicks-ass.net>
Date:	Fri, 3 Jul 2015 14:19:07 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Paolo Bonzini <pbonzini@...hat.com>
Cc:	Pontus Fuchs <pontus.fuchs@...il.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	mingo@...hat.com,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	gleb@...nel.org
Subject: Re: [PATCH] sched,kvm: Fix KVM preempt_notifier usage

On Fri, Jul 03, 2015 at 01:12:11PM +0200, Paolo Bonzini wrote:
> In fact you shouldn't have just tested the patch on a case _without_
> preemption notifiers, you should have also benchmarked the impact that
> static keys have _with_ preemption notifiers.  In a
> not-really-artificial case (one single-processor guest running on the
> host), the static key patch adds a static_key_slow_inc on a relatively
> hot path for KVM, which is not acceptable.

Spawning the first vcpu is a hot path?
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