Re: [PATCH RFC 0/2] kvm: Better yield_to candidate using preemption notifiers

[Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com>]

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.