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Date: Sun, 30 Sep 2012 10:24:51 +0200 From: Avi Kivity <avi@...hat.com> To: habanero@...ux.vnet.ibm.com CC: Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>, Peter Zijlstra <peterz@...radead.org>, "H. Peter Anvin" <hpa@...or.com>, Marcelo Tosatti <mtosatti@...hat.com>, Ingo Molnar <mingo@...hat.com>, Rik van Riel <riel@...hat.com>, Srikar <srikar@...ux.vnet.ibm.com>, "Nikunj A. Dadhania" <nikunj@...ux.vnet.ibm.com>, KVM <kvm@...r.kernel.org>, Jiannan Ouyang <ouyang@...pitt.edu>, chegu vinod <chegu_vinod@...com>, LKML <linux-kernel@...r.kernel.org>, Srivatsa Vaddagiri <srivatsa.vaddagiri@...il.com>, Gleb Natapov <gleb@...hat.com>, Andrew Jones <drjones@...hat.com> Subject: Re: [PATCH RFC 0/2] kvm: Improving undercommit,overcommit scenarios in PLE handler On 09/28/2012 01:40 PM, Andrew Theurer wrote: >> >> >> >> >> IIRC, with defer preemption : >> >> we will have hook in spinlock/unlock path to measure depth of lock held, >> >> and shared with host scheduler (may be via MSRs now). >> >> Host scheduler 'prefers' not to preempt lock holding vcpu. (or rather >> >> give say one chance. >> > >> > A downside is that we have to do that even when undercommitted. > > Hopefully vcpu preemption is very rare when undercommitted, so it should > not happen much at all. As soon as you're preempted, you're effectively overcommitted (even if the system as a whole is undercommitted). What I meant was that you need to communicate your lock state to the host, and with fine-grained locking this can happen a lot. It may be as simple as an increment/decrement instruction though. -- error compiling committee.c: too many arguments to function -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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