From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753195AbbC0Git (ORCPT ); Fri, 27 Mar 2015 02:38:49 -0400 Received: from e28smtp09.in.ibm.com ([122.248.162.9]:41955 "EHLO e28smtp09.in.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752649AbbC0Gir (ORCPT ); Fri, 27 Mar 2015 02:38:47 -0400 Message-ID: <5514FB70.4010600@linux.vnet.ibm.com> Date: Fri, 27 Mar 2015 12:10:48 +0530 From: Raghavendra K T Organization: IBM User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130625 Thunderbird/17.0.7 MIME-Version: 1.0 To: Peter Zijlstra CC: Waiman.Long@hp.com, tglx@linutronix.de, mingo@redhat.com, hpa@zytor.com, paolo.bonzini@gmail.com, konrad.wilk@oracle.com, boris.ostrovsky@oracle.com, paulmck@linux.vnet.ibm.com, riel@redhat.com, torvalds@linux-foundation.org, david.vrabel@citrix.com, oleg@redhat.com, scott.norton@hp.com, doug.hatch@hp.com, linux-arch@vger.kernel.org, x86@kernel.org, linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, xen-devel@lists.xenproject.org, kvm@vger.kernel.org, luto@amacapital.net Subject: Re: [PATCH 0/9] qspinlock stuff -v15 References: <20150316131613.720617163@infradead.org> In-Reply-To: <20150316131613.720617163@infradead.org> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 15032706-0033-0000-0000-000004F01086 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 03/16/2015 06:46 PM, Peter Zijlstra wrote: > Hi Waiman, > > As promised; here is the paravirt stuff I did during the trip to BOS last week. > > All the !paravirt patches are more or less the same as before (the only real > change is the copyright lines in the first patch). > > The paravirt stuff is 'simple' and KVM only -- the Xen code was a little more > convoluted and I've no real way to test that but it should be stright fwd to > make work. > > I ran this using the virtme tool (thanks Andy) on my laptop with a 4x > overcommit on vcpus (16 vcpus as compared to the 4 my laptop actually has) and > it both booted and survived a hackbench run (perf bench sched messaging -g 20 > -l 5000). > > So while the paravirt code isn't the most optimal code ever conceived it does work. > > Also, the paravirt patching includes replacing the call with "movb $0, %arg1" > for the native case, which should greatly reduce the cost of having > CONFIG_PARAVIRT_SPINLOCKS enabled on actual hardware. > > I feel that if someone were to do a Xen patch we can go ahead and merge this > stuff (finally!). > > These patches do not implement the paravirt spinlock debug stats currently > implemented (separately) by KVM and Xen, but that should not be too hard to do > on top and in the 'generic' code -- no reason to duplicate all that. > > Of course; once this lands people can look at improving the paravirt nonsense. > last time I had reported some hangs in kvm case, and I can confirm that the current set of patches works fine. Feel free to add Tested-by: Raghavendra K T #kvm pv As far as performance is concerned (with my 16core +ht machine having 16vcpu guests [ even w/ , w/o the lfsr hash patchset ]), I do not see any significant observations to report, though I understand that we could see much more benefit with large number of vcpus because of possible reduction in cache bouncing.