From mboxrd@z Thu Jan 1 00:00:00 1970 From: Raghavendra K T Subject: Re: [PATCH RFC V6 0/11] Paravirtualized ticketlocks Date: Thu, 29 Mar 2012 23:33:49 +0530 Message-ID: <4F74A405.2040609@linux.vnet.ibm.com> References: <20120321102041.473.61069.sendpatchset@codeblue.in.ibm.com> <4F707C5F.1000905@redhat.com> <4F716E31.3000803@linux.vnet.ibm.com> <4F73568D.7000703@linux.vnet.ibm.com> <4F743247.5080407@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii"; Format="flowed" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <4F743247.5080407@redhat.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: virtualization-bounces@lists.linux-foundation.org Errors-To: virtualization-bounces@lists.linux-foundation.org To: Avi Kivity Cc: KVM , Alan Meadows , Peter Zijlstra , Stefano Stabellini , the arch/x86 maintainers , LKML , Konrad Rzeszutek Wilk , Andi Kleen , Srivatsa Vaddagiri , Jeremy Fitzhardinge , "H. Peter Anvin" , Attilio Rao , Ingo Molnar , Virtualization , Linus Torvalds , Xen Devel , Stephan Diestelhorst List-Id: virtualization@lists.linuxfoundation.org On 03/29/2012 03:28 PM, Avi Kivity wrote: > On 03/28/2012 08:21 PM, Raghavendra K T wrote: >> >>> >>> >>> Looks like a good baseline on which to build the KVM >>> implementation. We >>> might need some handshake to prevent interference on the host >>> side with >>> the PLE code. >>> >> >> I think I still missed some point in Avi's comment. I agree that PLE >> may be interfering with above patches (resulting in less performance >> advantages). but we have not seen performance degradation with the >> patches in earlier benchmarks. [ theoretically since patch has very >> slight advantage over PLE that atleast it knows who should run next ]. > > The advantage grows with the vcpu counts and overcommit ratio. If you > have N vcpus and M:1 overcommit, PLE has to guess from N/M queued vcpus > while your patch knows who to wake up. > Yes. I agree. >> >> So TODO in my list on this is: >> 1. More analysis of performance on PLE mc. >> 2. Seeing how to implement handshake to increase performance (if PLE + >> patch combination have slight negative effect). > > I can think of two options: I really like below ideas. Thanks for that!. > - from the PLE handler, don't wake up a vcpu that is sleeping because it > is waiting for a kick How about, adding another pass in the beginning of kvm_vcpu_on_spin() to check if any vcpu is already kicked. This would almost result in yield_to(kicked_vcpu). IMO this is also worth trying. will try above ideas soon. > - look at other sources of pause loops (I guess smp_call_function() is > the significant source) and adjust them to use the same mechanism, and > ask the host to disable PLE exiting. > > This can be done incrementally later. > Yes.. this can wait a bit.