From mboxrd@z Thu Jan 1 00:00:00 1970 From: Raghavendra K T Subject: Re: [PATCH RFC V3 0/3] kvm: Improving directed yield in PLE handler Date: Fri, 13 Jul 2012 00:53:44 +0530 Message-ID: <4FFF2440.40807@linux.vnet.ibm.com> References: <20120712191712.30440.68944.sendpatchset@codeblue> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20120712191712.30440.68944.sendpatchset@codeblue> Sender: linux-kernel-owner@vger.kernel.org List-Archive: List-Post: To: S390 , Carsten Otte , Christian Borntraeger , linux390@de.ibm.com Cc: Raghavendra K T , "H. Peter Anvin" , Thomas Gleixner , Marcelo Tosatti , Ingo Molnar , Avi Kivity , Rik van Riel , KVM , chegu vinod , "Andrew M. Theurer" , LKML , X86 , Gleb Natapov , Srivatsa Vaddagiri , Joerg Roedel List-ID: On 07/13/2012 12:47 AM, Raghavendra K T wrote: > Currently Pause Loop Exit (PLE) handler is doing directed yield to a > random vcpu on pl-exit. We already have filtering while choosing > the candidate to yield_to. This change adds more checks while choosing > a candidate to yield_to. > > On a large vcpu guests, there is a high probability of > yielding to the same vcpu who had recently done a pause-loop exit. > Such a yield can lead to the vcpu spinning again. > > The patchset keeps track of the pause loop exit and gives chance to a > vcpu which has: > > (a) Not done pause loop exit at all (probably he is preempted lock-holder) > > (b) vcpu skipped in last iteration because it did pause loop exit, and > probably has become eligible now (next eligible lock holder) > > This concept also helps in cpu relax interception cases which use same handler. The patches are tested on x86 only since I don't have access to s390 machine. Please let me know if changes are ok on s390.