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Date: Wed, 28 Nov 2012 18:07:10 -0800 From: Chegu Vinod <chegu_vinod@...com> To: Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com> CC: Peter Zijlstra <peterz@...radead.org>, "H. Peter Anvin" <hpa@...or.com>, Avi Kivity <avi@...hat.com>, Gleb Natapov <gleb@...hat.com>, Ingo Molnar <mingo@...hat.com>, Marcelo Tosatti <mtosatti@...hat.com>, Rik van Riel <riel@...hat.com>, Srikar <srikar@...ux.vnet.ibm.com>, "Nikunj A. Dadhania" <nikunj@...ux.vnet.ibm.com>, KVM <kvm@...r.kernel.org>, Jiannan Ouyang <ouyang@...pitt.edu>, "Andrew M. Theurer" <habanero@...ux.vnet.ibm.com>, LKML <linux-kernel@...r.kernel.org>, Srivatsa Vaddagiri <srivatsa.vaddagiri@...il.com>, Andrew Jones <drjones@...hat.com> Subject: Re: [PATCH V3 RFC 0/2] kvm: Improving undercommit scenarios On 11/26/2012 4:07 AM, Raghavendra K T wrote: > In some special scenarios like #vcpu <= #pcpu, PLE handler may > prove very costly, because there is no need to iterate over vcpus > and do unsuccessful yield_to burning CPU. > > The first patch optimizes all the yield_to by bailing out when there > is no need to continue in yield_to (i.e., when there is only one task > in source and target rq). > > Second patch uses that in PLE handler. Further when a yield_to fails > we do not immediately go out of PLE handler instead we try thrice > to have better statistical possibility of false return. Otherwise that > would affect moderate overcommit cases. > > Result on 3.7.0-rc6 kernel shows around 140% improvement for ebizzy 1x and > around 51% for dbench 1x with 32 core PLE machine with 32 vcpu guest. > > > base = 3.7.0-rc6 > machine: 32 core mx3850 x5 PLE mc > > --+-----------+-----------+-----------+------------+-----------+ > ebizzy (rec/sec higher is beter) > --+-----------+-----------+-----------+------------+-----------+ > base stdev patched stdev %improve > --+-----------+-----------+-----------+------------+-----------+ > 1x 2511.3000 21.5409 6051.8000 170.2592 140.98276 > 2x 2679.4000 332.4482 2692.3000 251.4005 0.48145 > 3x 2253.5000 266.4243 2192.1667 178.9753 -2.72169 > 4x 1784.3750 102.2699 2018.7500 187.5723 13.13485 > --+-----------+-----------+-----------+------------+-----------+ > > --+-----------+-----------+-----------+------------+-----------+ > dbench (throughput in MB/sec. higher is better) > --+-----------+-----------+-----------+------------+-----------+ > base stdev patched stdev %improve > --+-----------+-----------+-----------+------------+-----------+ > 1x 6677.4080 638.5048 10098.0060 3449.7026 51.22643 > 2x 2012.6760 64.7642 2019.0440 62.6702 0.31639 > 3x 1302.0783 40.8336 1292.7517 27.0515 -0.71629 > 4x 3043.1725 3243.7281 4664.4662 5946.5741 53.27643 > --+-----------+-----------+-----------+------------+-----------+ > > Here is the refernce of no ple result. > ebizzy-1x_nople 7592.6000 rec/sec > dbench_1x_nople 7853.6960 MB/sec > > The result says we can still improve by 60% for ebizzy, but overall we are > getting impressive performance with the patches. > > Changes Since V2: > - Dropped global measures usage patch (Peter Zilstra) > - Do not bail out on first failure (Avi Kivity) > - Try thrice for the failure of yield_to to get statistically more correct > behaviour. > > Changes since V1: > - Discard the idea of exporting nrrunning and optimize in core scheduler (Peter) > - Use yield() instead of schedule in overcommit scenarios (Rik) > - Use loadavg knowledge to detect undercommit/overcommit > > Peter Zijlstra (1): > Bail out of yield_to when source and target runqueue has one task > > Raghavendra K T (1): > Handle yield_to failure return for potential undercommit case > > Please let me know your comments and suggestions. > > Link for V2: > https://lkml.org/lkml/2012/10/29/287 > > Link for V1: > https://lkml.org/lkml/2012/9/21/168 > > kernel/sched/core.c | 25 +++++++++++++++++++------ > virt/kvm/kvm_main.c | 26 ++++++++++++++++---------- > 2 files changed, 35 insertions(+), 16 deletions(-) > > . > Tested-by: Chegu Vinod <chegu_vinod@...com> -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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