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

[Raghavendra K T]

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

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