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SubjectRe: [PATCH V3 RFC 0/2] kvm: Improving undercommit scenarios
On 11/29/2012 07:37 AM, Chegu Vinod wrote:
> 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@hp.com>
>

Thanks for testing..



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