From mboxrd@z Thu Jan 1 00:00:00 1970 From: Rik van Riel Subject: Re: [PATCH RFC 0/2] kvm: Improving directed yield in PLE handler Date: Mon, 09 Jul 2012 18:28:03 -0400 Message-ID: <4FFB5AF3.4010805@redhat.com> References: <20120709062012.24030.37154.sendpatchset@codeblue> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20120709062012.24030.37154.sendpatchset@codeblue> Sender: linux-kernel-owner@vger.kernel.org List-Archive: List-Post: To: Raghavendra K T Cc: "H. Peter Anvin" , Thomas Gleixner , Marcelo Tosatti , Ingo Molnar , Avi Kivity , S390 , Carsten Otte , Christian Borntraeger , KVM , chegu vinod , "Andrew M. Theurer" , LKML , X86 , Gleb Natapov , linux390@de.ibm.com, Srivatsa Vaddagiri , Joerg Roedel List-ID: On 07/09/2012 02:20 AM, Raghavendra K T wrote: > Currently Pause Looop Exit (PLE) handler is doing directed yield to a > random VCPU on PL exit. Though we already have filtering while choosing > the candidate to yield_to, we can do better. > > Problem is, for large vcpu guests, we have more probability of yielding > to a bad vcpu. We are not able to prevent directed yield to same guy who > has done PL exit recently, who perhaps spins again and wastes CPU. > > Fix that by keeping track of who has done PL exit. So The Algorithm in series > give chance to a VCPU which has: > > (a) Not done PLE exit at all (probably he is preempted lock-holder) > > (b) VCPU skipped in last iteration because it did PL exit, and probably > has become eligible now (next eligible lock holder) > > Future enhancemnets: Your patch series looks good to me. Simple changes with a significant result. However, the simple heuristic could use some comments :) -- All rights reversed