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    SubjectRe: [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@hp.com>


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