Re: [PATCH] [RFC] timekeeping: Rework frequency adjustments to workbetter w/ nohz

From: Richard Cochran
Date: Tue Jan 28 2014 - 12:58:29 EST


I tested for a regression using the patched kernel with the nohz=off
command line option...

On Mon, Jan 13, 2014 at 10:15:18AM -0800, John Stultz wrote:
> On 01/13/2014 09:51 AM, Richard Cochran wrote:
> >
> > - Linux 3.12.7-nohz-plain-20140106 nohz-plain.log
> > - Linux 3.12.7-nohz-plain-20140106 NOHZ=OFF periodic-plain.log
> > - Linux 3.12.7-nohz-fix-20140106-00001-gd753140 nohz-fix.log

Regression check:

- Linux homeboy 3.12.7-nohz-fix-20140106-00001-gd753140 NOHZ=OFF
nohz-fix-periodic.log

> > The performance in the log files as reflected in the clock offset is
> > summarized in this table. The values are in nanoseconds.
> >
> > | | periodic-plain | nohz-fix | nohz-plain |
> > |---------+----------------+---------------+---------------|
> > | minimum | -1.599000e+03 | -1.051000e+03 | -5.373700e+04 |
> > | maximum | +1.311000e+03 | +1.048000e+03 | +6.389500e+04 |
> > | mean | +9.880240e-02 | -7.747305e+01 | +1.597904e+01 |
> > | stddev | +4.610021e+02 | +3.960978e+02 | +1.491263e+04 |

Comparing the nohz=off case with and without the patch, the three hour
test looks like this.

| | periodic-plain | nohz-fix-periodic |
|---------+----------------+-------------------+
| minimum | -1.599000e+03 | -1.427000e+03 |
| maximum | +1.311000e+03 | +1.279000e+03 |
| mean | +9.880240e-02 | -2.710778e+01 |
| stddev | +4.610021e+02 | +3.974372e+02 |

> > http://linuxptp.sourceforge.net/nohz-fix/current_nohz.png
> > http://linuxptp.sourceforge.net/nohz-fix/periodic_vs_fix.png

I also made a third graph showing before and after the patch.

http://linuxptp.sourceforge.net/nohz-fix/nohz_regression.png

> If you do get a chance to look again, I'd also be interested if running
> with nohz=off w/ the fix doesn't show any regression compared to the
> unmodified nohz=off case.

Looks like there is no regression.

Thanks,
Richard


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