linux-kernel - Re: [PATCH 0/5] perf/mm: Fix PERF_SAMPLE_*_PAGE

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Message-ID: <20201116165707.GI3121392@hirez.programming.kicks-ass.net>
Date:   Mon, 16 Nov 2020 17:57:07 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Dave Hansen <dave.hansen@...el.com>
Cc:     Matthew Wilcox <willy@...radead.org>,
        "Kirill A. Shutemov" <kirill@...temov.name>,
        kan.liang@...ux.intel.com, mingo@...nel.org, acme@...nel.org,
        mark.rutland@....com, alexander.shishkin@...ux.intel.com,
        jolsa@...hat.com, eranian@...gle.com, christophe.leroy@...roup.eu,
        npiggin@...il.com, linuxppc-dev@...ts.ozlabs.org,
        mpe@...erman.id.au, will@...nel.org, aneesh.kumar@...ux.ibm.com,
        sparclinux@...r.kernel.org, davem@...emloft.net,
        catalin.marinas@....com, linux-arch@...r.kernel.org,
        linux-kernel@...r.kernel.org, ak@...ux.intel.com,
        kirill.shutemov@...ux.intel.com
Subject: Re: [PATCH 0/5] perf/mm: Fix PERF_SAMPLE_*_PAGE_SIZE

On Mon, Nov 16, 2020 at 08:36:36AM -0800, Dave Hansen wrote:
> On 11/16/20 8:32 AM, Matthew Wilcox wrote:
> >>
> >> That's really the best we can do from software without digging into
> >> microarchitecture-specific events.
> > I mean this is perf.  Digging into microarch specific events is what it
> > does ;-)
> 
> Yeah, totally.

Sure, but the automatic promotion/demotion of TLB sizes is not visible
if you don't know what you startd out with.

> But, if we see a bunch of 4k TLB hit events, it's still handy to know
> that those 4k TLB hits originated from a 2M page table entry.  This
> series just makes sure that perf has the data about the page table
> mapping sizes regardless of what the microarchitecture does with it.

This.