Hi, Suppose 2 VMs both of which just has a single VCPU share a single PCPU, if I run CPU intensive program in both of the VMs, the percentage of CPU usage from xentop is almost 100% for both of the VMs. I got confusing because since 2 VCPU shares a single PCPU, the percentage for each one should be around 50%, which is the result if I change the scheduler from credit2 to credit. Does it because credit2 change something or is this a bug for xentop or credit2? Thanks, Yuehai _______________________________________________ Xen-devel mailing list Xen-devel@lists.xensource.com http://lists.xensource.com/xen-devel
I assume that your system has more than 1 PCPU, and that you''re using pinning to try to limit the VM to 1 PCPU? At the moment, the credit2 scheduler doesn''t implement pinning -- cpu affinity is entirely ignored. (It is an experimental scheduler, after all.) I think theoretically making pinning function shouldn''t be too hard; but making the credit algorithm work with an arbitrary combination of affinities would require some careful thinking, and might not even be possible. If you want, you can try to use cpu pools to isolate the two VMs to a single PCPU. I haven''t tried credit2 with pools yet, but in theory it should work. -George On 23/09/10 14:48, Yuehai Xu wrote:> Hi, > > Suppose 2 VMs both of which just has a single VCPU share a single > PCPU, if I run CPU intensive program in both of the VMs, the > percentage of CPU usage from xentop is almost 100% for both of the > VMs. I got confusing because since 2 VCPU shares a single PCPU, the > percentage for each one should be around 50%, which is the result if I > change the scheduler from credit2 to credit. > > Does it because credit2 change something or is this a bug for xentop or credit2? > > Thanks, > Yuehai_______________________________________________ Xen-devel mailing list Xen-devel@lists.xensource.com http://lists.xensource.com/xen-devel
On Fri, Sep 24, 2010 at 7:38 AM, George Dunlap <George.Dunlap@eu.citrix.com> wrote:> I assume that your system has more than 1 PCPU, and that you''re using > pinning to try to limit the VM to 1 PCPU?Yes, you are correct. In order to test the performance of credit2 for the problem of mix work load, I pin VCPUs from VMs to a PCPU while the VCPU of Dom0 pins to another PCPU.> > At the moment, the credit2 scheduler doesn''t implement pinning -- cpu > affinity is entirely ignored. (It is an experimental scheduler, after all.) > I think theoretically making pinning function shouldn''t be too hard; but > making the credit algorithm work with an arbitrary combination of affinities > would require some careful thinking, and might not even be possible. >So, the result that I got, which shows almost 100% usage of CPU for each VCPU, is actually because the VCPUs use different PCPUs instead of a single one, is that correct?> If you want, you can try to use cpu pools to isolate the two VMs to a single > PCPU. I haven''t tried credit2 with pools yet, but in theory it should work.Ok, I will try it and tell you the result once I get it. Thanks, Yuehai> > -George > > On 23/09/10 14:48, Yuehai Xu wrote: >> >> Hi, >> >> Suppose 2 VMs both of which just has a single VCPU share a single >> PCPU, if I run CPU intensive program in both of the VMs, the >> percentage of CPU usage from xentop is almost 100% for both of the >> VMs. I got confusing because since 2 VCPU shares a single PCPU, the >> percentage for each one should be around 50%, which is the result if I >> change the scheduler from credit2 to credit. >> >> Does it because credit2 change something or is this a bug for xentop or >> credit2? >> >> Thanks, >> Yuehai > >_______________________________________________ Xen-devel mailing list Xen-devel@lists.xensource.com http://lists.xensource.com/xen-devel
On Fri, Sep 24, 2010 at 3:14 PM, Yuehai Xu <yuehaixu@gmail.com> wrote:> So, the result that I got, which shows almost 100% usage of CPU for > each VCPU, is actually because the VCPUs use different PCPUs instead > of a single one, is that correct?Yes, that''s right.>> If you want, you can try to use cpu pools to isolate the two VMs to a single >> PCPU. I haven''t tried credit2 with pools yet, but in theory it should work. > > Ok, I will try it and tell you the result once I get it.Cool -- good luck! -George _______________________________________________ Xen-devel mailing list Xen-devel@lists.xensource.com http://lists.xensource.com/xen-devel