From mboxrd@z Thu Jan 1 00:00:00 1970 From: Zhiyuan Shao Subject: Re: Questions regarding Xen Credit Scheduler Date: Fri, 17 Dec 2010 22:25:53 +0800 Message-ID: <4D0B72F1.3080605@gmail.com> References: Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed 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: xen-devel@lists.xensource.com List-Id: xen-devel@lists.xenproject.org In your case, I think, you can try Boost-Credit. Your I/O intensive domain will benefit for that. Best, Zhiyuan On 07/09/2010 05:14 AM, Gaurav Dhiman wrote: > Hi All, > > I am using Xen 3.3.2 for some of my experiments, and have been > consistently observing some sub-optimal results in our experiments > with latency sensitive I/O intensive and compute bound VMs running > together on a physical machine. We are observing latency issues in > cases with enough CPU resources available for both the VMs to co-exist > well, even if we give much higher weight to the latency sensitive VM. > I suspect it is due to the way the Xen credit scheduler works. In this > context, I have some questions regarding the scheduler: > > 1) In the sched_acct function, the credit cap is set to 300, enough to > survive one time slice. But if some VCPU crosses that cap, it is set > to 0, and marked inactive. Why is there no concept of a ceiling (like > that of a floor for the VCPUs going over the credit line), i.e. why is > it not set to 300? Is there some fundamental reason for setting it to > 0? I believe this is resulting in a lot of times when our latency > sensitive VCPUs have to wait for maybe a time slice, when they can > immediately run. This might happen if they run with BOOST priority and > get interrupted by a timer tick, which takes that priority away. > > 2) Why is the runq sorted by just priority (which is very coarse > grained: BOOST, UNDER and OVER), and not the credit? This can result > in VCPUs with higher credit getting starved for CPU if we have batch > and latency sensitive VCPUs in the system. > > 3) Is there some patch, which makes the current credit scheduler > fairer to the latency sensitive VCPUs? I see that the sched_credit2 > scheduler addresses these issues, but right now it has just one global > runq and no load balancing features. > > Any advice/inputs here will be extremely valuable! > > Thanks in advance, > -Gaurav > > _______________________________________________ > Xen-devel mailing list > Xen-devel@lists.xensource.com > http://lists.xensource.com/xen-devel