linux-kernel - RE: [LKP] Re: [perf/x86] 81ec3f3c4c: will-it-scale.per_process

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Date:   Sat, 22 Feb 2020 17:08:20 +0000
From:   "Kleen, Andi" <andi.kleen@...el.com>
To:     "Tang, Feng" <feng.tang@...el.com>
CC:     Peter Zijlstra <peterz@...radead.org>,
        "Chen, Rong A" <rong.a.chen@...el.com>,
        Jiri Olsa <jolsa@...hat.com>, Ingo Molnar <mingo@...nel.org>,
        Vince Weaver <vincent.weaver@...ne.edu>,
        Jiri Olsa <jolsa@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Arnaldo Carvalho de Melo <acme@...hat.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        "Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>,
        Ravi Bangoria <ravi.bangoria@...ux.ibm.com>,
        Stephane Eranian <eranian@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>,
        "lkp@...ts.01.org" <lkp@...ts.01.org>,
        "Huang, Ying" <ying.huang@...el.com>
Subject: RE: [LKP] Re: [perf/x86] 81ec3f3c4c: will-it-scale.per_process_ops
 -5.5% regression

>Thanks for the suggestion, I tried this and the 5.5 regrssion is gone!
>which also confirms the offset for the bulk of stuff following "pmu"
>causes the performance drop.

Okay that confirms that it is false sharing. Looking at c2c is the right way to
go then.

Peter, could adopt the padding as a workaround for now?

-Andi