linux-kernel - Re: 'perf test tsc' failing, bisected to "sched/clock: Provide better clock continuity"

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Message-ID: <20170316145311.4daeysai4r3vunlv@hirez.programming.kicks-ass.net>
Date:   Thu, 16 Mar 2017 15:53:11 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:     Adrian Hunter <adrian.hunter@...el.com>,
        Jiri Olsa <jolsa@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Wang Nan <wangnan0@...wei.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: 'perf test tsc' failing, bisected to "sched/clock: Provide
 better clock continuity"

On Thu, Mar 16, 2017 at 11:01:03AM -0300, Arnaldo Carvalho de Melo wrote:
> Hi, this entry is failing for a while:
> 
> [root@...et ~]# perf test -v tsc
> 55: Convert perf time to TSC                   :
> --- start ---
> test child forked, pid 3008
> mmap size 528384B
> 1st event perf time 93133455486631 tsc 15369449468752
> rdtsc          time 93133464598760 tsc 15369473104358
> 2nd event perf time 93133455506961 tsc 15369449521485
> test child finished with -1
> ---- end ----
> Convert perf time to TSC: FAILED!
> [root@...et ~]#
> 
> I bisected it to the following kernel change, ideas?
> 
> [acme@...icio linux]$ git bisect good
> 5680d8094ffa9e5cfc81afdd865027ee6417c263 is the first bad commit
> commit 5680d8094ffa9e5cfc81afdd865027ee6417c263
> Author: Peter Zijlstra <peterz@...radead.org>
> Date:   Thu Dec 15 13:36:17 2016 +0100
> 
>     sched/clock: Provide better clock continuity

Right, ahunter also complained about this. I had a half arsed fugly
patch in the works. Let me see if I can improve and finish.