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SubjectRe: [PATCH RFC 0/2] kvm: Better yield_to candidate using preemption notifiers
On 03/08/2013 12:40 AM, Marcelo Tosatti wrote:
> On Mon, Mar 04, 2013 at 11:31:46PM +0530, Raghavendra K T wrote:
>> This patch series further filters better vcpu candidate to yield to
>> in PLE handler. The main idea is to record the preempted vcpus using
>> preempt notifiers and iterate only those preempted vcpus in the
>> handler. Note that the vcpus which were in spinloop during pause loop
>> exit are already filtered.
>>
>> Thanks Jiannan, Avi for bringing the idea and Gleb, PeterZ for
>> precious suggestions during the discussion.
>> Thanks Srikar for suggesting to avoid rcu lock while checking task state
>> that has improved overcommit cases.
>>
>> There are basically two approches for the implementation.
>>
>> Method 1: Uses per vcpu preempt flag (this series).
>>
>> Method 2: We keep a bitmap of preempted vcpus. using this we can easily
>> iterate over preempted vcpus.
>>
>> Note that method 2 needs an extra index variable to identify/map bitmap to
>> vcpu and it also needs static vcpu allocation.
>>
>> I am also posting Method 2 approach for reference in case it interests.
>>
>> Result: decent improvement for kernbench and ebizzy.
>>
>> base = 3.8.0 + undercommit patches
>> patched = base + preempt patches
>>
>> Tested on 32 core (no HT) mx3850 machine with 32 vcpu guest 8GB RAM
>>
>> --+-----------+-----------+-----------+------------+-----------+
>> kernbench (exec time in sec lower is beter)
>> --+-----------+-----------+-----------+------------+-----------+
>> base stdev patched stdev %improve
>> --+-----------+-----------+-----------+------------+-----------+
>> 1x 47.0383 4.6977 44.2584 1.2899 5.90986
>> 2x 96.0071 7.1873 91.2605 7.3567 4.94401
>> 3x 164.0157 10.3613 156.6750 11.4267 4.47561
>> 4x 212.5768 23.7326 204.4800 13.2908 3.80888
>> --+-----------+-----------+-----------+------------+-----------+
>> no ple kernbench 1x result for reference: 46.056133
>>
>> --+-----------+-----------+-----------+------------+-----------+
>> ebizzy (record/sec higher is better)
>> --+-----------+-----------+-----------+------------+-----------+
>> base stdev patched stdev %improve
>> --+-----------+-----------+-----------+------------+-----------+
>> 1x 5609.2000 56.9343 6263.7000 64.7097 11.66833
>> 2x 2071.9000 108.4829 2653.5000 181.8395 28.07085
>> 3x 1557.4167 109.7141 1993.5000 166.3176 28.00043
>> 4x 1254.7500 91.2997 1765.5000 237.5410 40.70532
>> --+-----------+-----------+-----------+------------+-----------+
>> no ple ebizzy 1x result for reference : 7394.9 rec/sec
>>
>> Please let me know if you have any suggestions and comments.
>>
>> Raghavendra K T (2):
>> kvm: Record the preemption status of vcpus using preempt notifiers
>> kvm: Iterate over only vcpus that are preempted
>
> Reviewed-by: Marcelo Tosatti <mtosatti@redhat.com>
>

Thank you Marcelo.



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