From mboxrd@z Thu Jan  1 00:00:00 1970
From: Cyril Hrubis <chrubis@suse.cz>
Date: Tue, 23 May 2017 11:16:08 +0200
Subject: [LTP] [PATCH v2] [RFC] pselect01: Tune thresholds
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Hi!
> > Hmm, strange, it looks like for 100us we got more or less all samples
> > close to 160us but for 500us half of the samples are close to 560us and
> > about 400 is more than 1000us, that does not look right. I wonder what
> > happens there. And the same for the rest of the measurements everything
> > but 100us sleeps has two peaks that are more or less 500us apart. So far
> > my machines, even VMs, had one peak and some outliners.
> > 
> > Can you try to rerun the test with a realtime priority?
> 
> Ran as "chrt -f 50 ./measure", results attached.
> 

Looks more or less the same and I still cannot reproduce the issue on
any of the machines I have here.

Looking at errata for AMD cpus #778 says that TSC may drift under some
circumstances:
http://support.amd.com/TechDocs/51810_16h_00h-0Fh_Rev_Guide.pdf#unique_29

Can you try to disable P-state in BIOS or set cpufreq to performance?

-- 
Cyril Hrubis
chrubis@suse.cz