Messages in this thread | | | Date | Fri, 05 Oct 2012 14:36:43 +0530 | From | Raghavendra K T <> | Subject | Re: [PATCH RFC 1/2] kvm: Handle undercommitted guest case in PLE handler |
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On 10/04/2012 08:11 PM, Andrew Theurer wrote: > On Thu, 2012-10-04 at 14:41 +0200, Avi Kivity wrote: >> On 10/04/2012 12:49 PM, Raghavendra K T wrote: >>> On 10/03/2012 10:35 PM, Avi Kivity wrote: >>>> On 10/03/2012 02:22 PM, Raghavendra K T wrote: >>>>>> So I think it's worth trying again with ple_window of 20000-40000. >>>>>> >>>>> >>>>> Hi Avi, >>>>> >>>>> I ran different benchmarks increasing ple_window, and results does not >>>>> seem to be encouraging for increasing ple_window. >>>> >>>> Thanks for testing! Comments below. >>>> >>>>> Results: >>>>> 16 core PLE machine with 16 vcpu guest. >>>>> >>>>> base kernel = 3.6-rc5 + ple handler optimization patch >>>>> base_pleopt_8k = base kernel + ple window = 8k >>>>> base_pleopt_16k = base kernel + ple window = 16k >>>>> base_pleopt_32k = base kernel + ple window = 32k >>>>> >>>>> >>>>> Percentage improvements of benchmarks w.r.t base_pleopt with >>>>> ple_window = 4096 >>>>> >>>>> base_pleopt_8k base_pleopt_16k base_pleopt_32k >>>>> ----------------------------------------------------------------- >>>>> >>>>> kernbench_1x -5.54915 -15.94529 -44.31562 >>>>> kernbench_2x -7.89399 -17.75039 -37.73498 >>>> >>>> So, 44% degradation even with no overcommit? That's surprising. >>> >>> Yes. Kernbench was run with #threads = #vcpu * 2 as usual. Is it >>> spending 8 times the original ple_window cycles for 16 vcpus >>> significant? >> >> A PLE exit when not overcommitted cannot do any good, it is better to >> spin in the guest rather that look for candidates on the host. In fact >> when we benchmark we often disable PLE completely. > > Agreed. However, I really do not understand why the kernbench regressed > with bigger ple_window. It should stay the same or improve. Raghu, do > you have perf data for the kernbench runs?
Andrew, No. 'll get this with perf kvm.
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