Robinson, Eric
2009-Mar-25 17:37 UTC
[Xen-users] Why is Processor Utilization So High within the DomU?
We have a 12-core Xeon server with 32GB RAM. On it we have a 1-VCPU DomU running a Windows 2003 Std. R2 terminal server. When I run PerfMon within Windows, I see that processor utilization runs very high, on average 30-50%. Before we virtualized this server, it was running on a 4-core machine with 16GB RAM and processor utilization averaged 5-20%. Why so much higher now in a DomU environment? -- Eric Robinson Disclaimer - March 25, 2009 This email and any files transmitted with it are confidential and intended solely for xen-users@lists.xensource.com. If you are not the named addressee you should not disseminate, distribute, copy or alter this email. Any views or opinions presented in this email are solely those of the author and might not represent those of Physician Select Management and Physician''s Managed Care. Warning: Although Physician Select Management and Physician''s Managed Care have taken reasonable precautions to ensure no viruses are present in this email, the companies cannot accept responsibility for any loss or damage arising from the use of this email or attachments. This disclaimer was added by Policy Patrol: http://www.policypatrol.com/ _______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users
Javier Guerra
2009-Mar-25 17:41 UTC
Re: [Xen-users] Why is Processor Utilization So High within the DomU?
On Wed, Mar 25, 2009 at 12:37 PM, Robinson, Eric <eric.robinson@psmnv.com>wrote:> > We have a 12-core Xeon server with 32GB RAM. On it we have a 1-VCPU DomU > running a Windows 2003 Std. R2 terminal server. When I run PerfMon > within Windows, I see that processor utilization runs very high, on > average 30-50%. Before we virtualized this server, it was running on a > 4-core machine with 16GB RAM and processor utilization averaged 5-20%. > Why so much higher now in a DomU environment?if it was 5-20% on a 4-core, a naïve calculation means going to a 1-core (virtual or not) should get 20-80% doesn''t sound so far off -- Javier _______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users
Thiago Camargo Martins Cordeiro
2009-Mar-25 17:46 UTC
Re: [Xen-users] Why is Processor Utilization So High within the DomU?
Yeah! I agree! 2009/3/25 Javier Guerra <javier@guerrag.com>> > > On Wed, Mar 25, 2009 at 12:37 PM, Robinson, Eric <eric.robinson@psmnv.com>wrote: > >> >> We have a 12-core Xeon server with 32GB RAM. On it we have a 1-VCPU DomU >> running a Windows 2003 Std. R2 terminal server. When I run PerfMon >> within Windows, I see that processor utilization runs very high, on >> average 30-50%. Before we virtualized this server, it was running on a >> 4-core machine with 16GB RAM and processor utilization averaged 5-20%. >> Why so much higher now in a DomU environment? > > > > if it was 5-20% on a 4-core, a naïve calculation means going to a 1-core > (virtual or not) should get 20-80% > > doesn''t sound so far off > > > -- > Javier > > _______________________________________________ > Xen-users mailing list > Xen-users@lists.xensource.com > http://lists.xensource.com/xen-users >_______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users
Javier Guerra
2009-Mar-25 22:26 UTC
Re: [Xen-users] Why is Processor Utilization So High within the DomU?
On Wed, Mar 25, 2009 at 5:05 PM, Robinson, Eric <eric.robinson@psmnv.com> wrote:> Interesting. I''m just trying to avoid wasting physical core time. If my > DomU has 2 VCPUs, and they are assigned to run on physical cores 1 and 2 > respectively, then it it possible to have another DomU with 2 VCPUs that > are assigned to use the same 2 physical cores?(please don''t take discussions off-list unless it''s too offtopic, i''m ''re-on-list-ing'' the thread) yes, a real cpu can emulate several vCPUs. that''s the only way to virtualise when you have a single core (yes, there was a time when most machines had a single CPU). even more, if you don''t pin the vCPUs to specific CPUs, they''ll be switched around. there''s some ''processor affinity'' that makes stay in the same CPU whenever possible, but if the load gets too unbalanced, it would be picked by other CPU. just like processes in a multitasking OS. and, like processes, if they fight for CPU, they''ll get some fraction of the prize. you can think of each vCPU as a ''thread'' on a multitasking OS. a single-vCPU VM is like a single-threaded process. so, adding more CPUs to the OS won''t make the task any faster. likewise, having more threads than CPUs means they can''t get a whole CPU each. of course, the CPU isn''t the only bottleneck, so when you have several VMs running, and the total number of vCPUs is equal to the number of real CPUs, you won''t see total 100% processor load. some (most?) of the time, those vCPUs would be wainting for I/O.> > -- > Eric Robinson > > > -----Original Message----- > From: Javier Guerra [mailto:javier@guerrag.com] > Sent: Wednesday, March 25, 2009 1:04 PM > To: Robinson, Eric > Subject: Re: [Xen-users] Why is Processor Utilization So High within the > DomU? > > On Wed, Mar 25, 2009 at 2:36 PM, Robinson, Eric > <eric.robinson@psmnv.com> wrote: >> I thought the 1 VCPU had access to all the physical cores? > > nope. > > if that were possible, it would be the answer to all the multithreading > development chores. just write for one CPU, mount on a wonderVM with a > ''megaVCPU'' on top of lots of CPUs and you''d get magical paralelization! > > unfortunately, CPU time isn''t a fluid quantity like water, or electical > power. you can''t put several CPUs to do one linear job (like emulating > a vCPU) faster, it has to be a parallelizable job (like emulating > several vCPUs) > > -- > Javier-- Javier _______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users