From mboxrd@z Thu Jan 1 00:00:00 1970 From: Juergen Gross Subject: Re: [Patch 0 of 2]: PV-domain SMP performance Date: Wed, 17 Dec 2008 15:20:16 +0100 Message-ID: <49490AA0.3080703@fujitsu-siemens.com> References: Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xensource.com Errors-To: xen-devel-bounces@lists.xensource.com To: Keir Fraser Cc: "xen-devel@lists.xensource.com" List-Id: xen-devel@lists.xenproject.org Keir Fraser wrote: > On 17/12/2008 12:21, "Juergen Gross" > wrote: > >> This result was achieved by avoiding descheduling of a vcpu only when irqs >> are blocked. Even better results might be possible with some fine tuning >> (e.g. instrumenting bh_enable/bh_disable). >> I think system time has dropped remarkably! > > It's nice, but it'd be more compelling if a win was shown on a real > benchmark. Under normal workloads there is actually little lock contention > in the Linux kernel, and hence I think scope for wins are limited. > > Also, pv_ops Linux already has some extra smartness in its spinlock > implementation. A spinner will sleep after some time, making it more likely > that the lock holder will run (who then wakes the sleeper when the lock is > released). You'd need to compare with that approach (which required no extra > hypervisor interfaces). Sure, my benchmark is a very special case :-) The advantage of my solution is a general mechanism to avoid preemption of a vcpu in critical sections instead of dealing with it after it has occured. Is the pv_ops Linux capable to deal with held locks in interrupt handling? What about other code paths which should be completed in short time? About real world applications: Again 4 vcpus pinned to one physical cpu, 3 files copied via scp to the test machine at the same time, each file about 50 MB. Linux-xen from xensource: about 1:50 elapsed time for each job My modified Linux: about 0:50 elapsed time Juergen -- Juergen Gross Principal Developer IP SW OS6 Telephone: +49 (0) 89 636 47950 Fujitsu Siemens Computers e-mail: juergen.gross@fujitsu-siemens.com Otto-Hahn-Ring 6 Internet: www.fujitsu-siemens.com D-81739 Muenchen Company details: www.fujitsu-siemens.com/imprint.html