Re: [PATCH RFC 1/2] kvm: Handle undercommitted guest case in PLE handler

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

On 10/18/2012 06:09 PM, Avi Kivity wrote:
> On 10/09/2012 08:51 PM, Raghavendra K T wrote:
>> Here is the summary:
>> We do get good benefit by increasing ple window. Though we don't
>> see good benefit for kernbench and sysbench, for ebizzy, we get huge
>> improvement for 1x scenario. (almost 2/3rd of ple disabled case).
>>
>> Let me know if you think we can increase the default ple_window
>> itself to 16k.
>>
>
> I think so, there is no point running with untuned defaults.
>

Oaky.

>>
>> I can respin the whole series including this default ple_window change.
>
> It can come as a separate patch.

Yes. Will spin it separately.

>
>>
>> I also have the perf kvm top result for both ebizzy and kernbench.
>> I think they are in expected lines now.
>>
>> Improvements
>> ================
>>
>> 16 core PLE machine with 16 vcpu guest
>>
>> base = 3.6.0-rc5 + ple handler optimization patches
>> base_pleopt_16k = base + ple_window = 16k
>> base_pleopt_32k = base + ple_window = 32k
>> base_pleopt_nople = base + ple_gap = 0
>> kernbench, hackbench, sysbench (time in sec lower is better)
>> ebizzy (rec/sec higher is better)
>>
>> % improvements w.r.t base (ple_window = 4k)
>> ---------------+---------------+-----------------+-------------------+
>>                 |base_pleopt_16k| base_pleopt_32k | base_pleopt_nople |
>> ---------------+---------------+-----------------+-------------------+
>> kernbench_1x   |  0.42371      |  1.15164        |   0.09320         |
>> kernbench_2x   | -1.40981      | -17.48282       |  -570.77053       |
>> ---------------+---------------+-----------------+-------------------+
>> sysbench_1x    | -0.92367      | 0.24241         | -0.27027          |
>> sysbench_2x    | -2.22706      |-0.30896         | -1.27573          |
>> sysbench_3x    | -0.75509      | 0.09444         | -2.97756          |
>> ---------------+---------------+-----------------+-------------------+
>> ebizzy_1x      | 54.99976      | 67.29460        |  74.14076         |
>> ebizzy_2x      | -8.83386      |-27.38403        | -96.22066         |
>> ---------------+---------------+-----------------+-------------------+
>
> So it seems we want dynamic PLE windows.  As soon as we enter overcommit
> we need to decrease the window.
>

Okay.
I have some rough idea on the implementation. I 'll try that after this
V2 experiments are over.
So in brief, I have this in my queue priority wise

1) V2 version of this patch series( in progress)
2) default PLE window
3) preemption notifiers
4) Pv spinlock