linux-kernel - Re: [PATCH] perf/x86: fix event counter update issue

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Message-ID: <20170222191848.GE1712@tassilo.jf.intel.com>
Date:   Wed, 22 Feb 2017 11:18:48 -0800
From:   Andi Kleen <ak@...ux.intel.com>
To:     "Liang, Kan" <kan.liang@...el.com>
Cc:     Vince Weaver <vincent.weaver@...ne.edu>,
        Peter Zijlstra <peterz@...radead.org>,
        "Odzioba, Lukasz" <lukasz.odzioba@...el.com>,
        Stephane Eranian <eranian@...gle.com>,
        "mingo@...hat.com" <mingo@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>
Subject: Re: [PATCH] perf/x86: fix event counter update issue

> No. It related to the counter width. The number of bits we can use should be
> 1 bit less than the total width. Otherwise, there will be problem.
> For big cores such as haswell, broadwell, skylake, the counter width is 48 bit.
> So we can only use 47 bits.
> For Silvermont and KNL, the counter width is only 32 bit I think. So we can only
> use 31 bits.

It is 40 bits on these cores, so 39bits.

-Andi