* Re: [Fwd: Re: [RFC -v3 PATCH 2/3] sched: add yield_to function] [not found] <1294164920.6169.199.camel@Palantir> @ 2011-01-04 23:38 ` Tommaso Cucinotta 2011-01-04 23:40 ` Tommaso Cucinotta 2011-01-05 9:41 ` Peter Zijlstra 0 siblings, 2 replies; 4+ messages in thread From: Tommaso Cucinotta @ 2011-01-04 23:38 UTC (permalink / raw) To: Peter Zijlstra, a.p.zijlstra Cc: Dario Faggioli, Dhaval Giani, Fabio Checconi, riel, Hillf Danton, kvm, linux-kernel, Avi Kiviti, Srivatsa Vaddagiri, Mike Galbraith, Chris Wright Il 04/01/2011 19:15, Dario Faggioli ha scritto: > > -------- Forwarded Message -------- > From: Peter Zijlstra<a.p.zijlstra@chello.nl> > To: Rik van Riel<riel@redhat.com> > Cc: Hillf Danton<dhillf@gmail.com>,kvm@vger.kernel.org, > linux-kernel@vger.kernel.org, Avi Kiviti<avi@redhat.com>, Srivatsa > Vaddagiri<vatsa@linux.vnet.ibm.com>, Mike Galbraith<efault@gmx.de>, > Chris Wright<chrisw@sous-sol.org> > Subject: Re: [RFC -v3 PATCH 2/3] sched: add yield_to function > Date: Tue, 04 Jan 2011 19:05:54 +0100 > RT guests don't make sense, there's nowhere near enough infrastructure > for that to work well. > > I'd argue that KVM running with RT priority is a bug. Peter, can I ask why did you state that ? In the IRMOS project, we are just deploying KVM VMs by using the Fabio's real-time scheduler (for others, a.k.a., the Fabio's EDF throttling patch, or IRMOS RT scheduler) in order to let the VMs get precise CPU scheduling guarantees by the kernel. So, in this context we do have KVM running at RT priority, and we do have experimental results showing how this can improve stability of performance of the hosted guest VMs. Of course, don't misunderstand me: this is a necessary condition for a stable performance of KVM VMs, I'm not saying it is sufficient for -- Tommaso Cucinotta, Computer Engineering PhD, Researcher ReTiS Lab, Scuola Superiore Sant'Anna, Pisa, Italy Tel +39 050 882 024, Fax +39 050 882 003 http://retis.sssup.it/people/tommaso ^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [Fwd: Re: [RFC -v3 PATCH 2/3] sched: add yield_to function] 2011-01-04 23:38 ` [Fwd: Re: [RFC -v3 PATCH 2/3] sched: add yield_to function] Tommaso Cucinotta @ 2011-01-04 23:40 ` Tommaso Cucinotta 2011-01-05 9:41 ` Peter Zijlstra 1 sibling, 0 replies; 4+ messages in thread From: Tommaso Cucinotta @ 2011-01-04 23:40 UTC (permalink / raw) To: Tommaso Cucinotta Cc: Peter Zijlstra, a.p.zijlstra, Dario Faggioli, Dhaval Giani, Fabio Checconi, riel, Hillf Danton, kvm, linux-kernel, Avi Kiviti, Srivatsa Vaddagiri, Mike Galbraith, Chris Wright Il 05/01/2011 00:38, Tommaso Cucinotta ha scritto: > Of course, don't misunderstand me: this is a necessary condition for a > stable performance of KVM VMs, I'm not saying it is sufficient for > ... it. Please, comment on this (reply to all, please, I'm not following LKML). Thanks, Tommaso ^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [Fwd: Re: [RFC -v3 PATCH 2/3] sched: add yield_to function] 2011-01-04 23:38 ` [Fwd: Re: [RFC -v3 PATCH 2/3] sched: add yield_to function] Tommaso Cucinotta 2011-01-04 23:40 ` Tommaso Cucinotta @ 2011-01-05 9:41 ` Peter Zijlstra 2011-01-06 13:28 ` Hillf Danton 1 sibling, 1 reply; 4+ messages in thread From: Peter Zijlstra @ 2011-01-05 9:41 UTC (permalink / raw) To: Tommaso Cucinotta Cc: Dario Faggioli, Dhaval Giani, Fabio Checconi, riel, Hillf Danton, kvm, linux-kernel, Avi Kiviti, Srivatsa Vaddagiri, Mike Galbraith, Chris Wright On Wed, 2011-01-05 at 00:38 +0100, Tommaso Cucinotta wrote: > Il 04/01/2011 19:15, Dario Faggioli ha scritto: > > > > -------- Forwarded Message -------- > > From: Peter Zijlstra<a.p.zijlstra@chello.nl> > > To: Rik van Riel<riel@redhat.com> > > Cc: Hillf Danton<dhillf@gmail.com>,kvm@vger.kernel.org, > > linux-kernel@vger.kernel.org, Avi Kiviti<avi@redhat.com>, Srivatsa > > Vaddagiri<vatsa@linux.vnet.ibm.com>, Mike Galbraith<efault@gmx.de>, > > Chris Wright<chrisw@sous-sol.org> > > Subject: Re: [RFC -v3 PATCH 2/3] sched: add yield_to function > > Date: Tue, 04 Jan 2011 19:05:54 +0100 > > RT guests don't make sense, there's nowhere near enough infrastructure > > for that to work well. > > > > I'd argue that KVM running with RT priority is a bug. > Peter, can I ask why did you state that ? In the IRMOS project, we > are just deploying KVM VMs by using the Fabio's real-time scheduler > (for others, a.k.a., the Fabio's EDF throttling patch, or IRMOS RT > scheduler) > in order to let the VMs get precise CPU scheduling guarantees by the > kernel. So, in this context we do have KVM running at RT priority, and > we do have experimental results showing how this can improve stability > of performance of the hosted guest VMs. > Of course, don't misunderstand me: this is a necessary condition for a > stable performance of KVM VMs, I'm not saying it is sufficient for I was mostly referring to the existing RT cruft (SCHED_RR/FIFO), that's utterly useless for KVM. As to hosting vcpus with CBS this might maybe make sense, but RT-guests are still miles away. Anyway, I'm not quite sure how you would want to deal with the guest spinlock issue in CBS, ideally you'd use paravirt guests to avoid that whole problem. Anyway, /me goes do something useful, virt sucks and should be taken out back and shot in the head. ^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [Fwd: Re: [RFC -v3 PATCH 2/3] sched: add yield_to function] 2011-01-05 9:41 ` Peter Zijlstra @ 2011-01-06 13:28 ` Hillf Danton 0 siblings, 0 replies; 4+ messages in thread From: Hillf Danton @ 2011-01-06 13:28 UTC (permalink / raw) To: Peter Zijlstra Cc: Tommaso Cucinotta, Dario Faggioli, Dhaval Giani, Fabio Checconi, riel, kvm, linux-kernel, Avi Kiviti, Srivatsa Vaddagiri, Mike Galbraith, Chris Wright, Mike Christie On Wed, Jan 5, 2011 at 5:41 PM, Peter Zijlstra <peterz@infradead.org> wrote: > On Wed, 2011-01-05 at 00:38 +0100, Tommaso Cucinotta wrote: >> Il 04/01/2011 19:15, Dario Faggioli ha scritto: >> > >> > -------- Forwarded Message -------- >> > From: Peter Zijlstra<a.p.zijlstra@chello.nl> >> > To: Rik van Riel<riel@redhat.com> >> > Cc: Hillf Danton<dhillf@gmail.com>,kvm@vger.kernel.org, >> > linux-kernel@vger.kernel.org, Avi Kiviti<avi@redhat.com>, Srivatsa >> > Vaddagiri<vatsa@linux.vnet.ibm.com>, Mike Galbraith<efault@gmx.de>, >> > Chris Wright<chrisw@sous-sol.org> >> > Subject: Re: [RFC -v3 PATCH 2/3] sched: add yield_to function >> > Date: Tue, 04 Jan 2011 19:05:54 +0100 >> > RT guests don't make sense, there's nowhere near enough infrastructure >> > for that to work well. >> > >> > I'd argue that KVM running with RT priority is a bug. >> Peter, can I ask why did you state that ? In the IRMOS project, we >> are just deploying KVM VMs by using the Fabio's real-time scheduler >> (for others, a.k.a., the Fabio's EDF throttling patch, or IRMOS RT >> scheduler) >> in order to let the VMs get precise CPU scheduling guarantees by the >> kernel. So, in this context we do have KVM running at RT priority, and >> we do have experimental results showing how this can improve stability >> of performance of the hosted guest VMs. >> Of course, don't misunderstand me: this is a necessary condition for a >> stable performance of KVM VMs, I'm not saying it is sufficient for > > I was mostly referring to the existing RT cruft (SCHED_RR/FIFO), that's > utterly useless for KVM. > > As to hosting vcpus with CBS this might maybe make sense, but RT-guests > are still miles away. Anyway, I'm not quite sure how you would want to > deal with the guest spinlock issue in CBS, ideally you'd use paravirt > guests to avoid that whole problem. > > Anyway, /me goes do something useful, virt sucks and should be taken out > back and shot in the head. > I dont think we are now still in the track of the patch from Rik, in which Mike brought the yield_to method into scheduling. The focus, as I see, is mainly on the effectiveness of the new method, since it could also be utilized in other environments, though currently it has nothing to do with the RT cruft but aims at easing certain lock contention in KVM. Another issue is that the change in the fair scheduling class, accompanying the new method, is deserved, for any reason Rik hold. Lets please return to the patch, and defer the RT. thanks Hillf ^ permalink raw reply [flat|nested] 4+ messages in thread
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[not found] <1294164920.6169.199.camel@Palantir>
2011-01-04 23:38 ` [Fwd: Re: [RFC -v3 PATCH 2/3] sched: add yield_to function] Tommaso Cucinotta
2011-01-04 23:40 ` Tommaso Cucinotta
2011-01-05 9:41 ` Peter Zijlstra
2011-01-06 13:28 ` Hillf Danton
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