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

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Date:   Mon, 16 Nov 2020 17:55:04 +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 08:28:23AM -0800, Dave Hansen wrote:
> On 11/16/20 7:54 AM, Matthew Wilcox wrote:
> > It gets even more complicated with CPUs with multiple levels of TLB
> > which support different TLB entry sizes.  My CPU reports:
> > 
> > TLB info
> >  Instruction TLB: 2M/4M pages, fully associative, 8 entries
> >  Instruction TLB: 4K pages, 8-way associative, 64 entries
> >  Data TLB: 1GB pages, 4-way set associative, 4 entries
> >  Data TLB: 4KB pages, 4-way associative, 64 entries
> >  Shared L2 TLB: 4KB/2MB pages, 6-way associative, 1536 entries
> 
> It's even "worse" on recent AMD systems.  Those will coalesce multiple
> adjacent PTEs into a single TLB entry.  I think Alphas did something
> like this back in the day with an opt-in.
> 
> Anyway, the changelog should probably replace:

ARM64 does too.

> > This enables PERF_SAMPLE_{DATA,CODE}_PAGE_SIZE to report accurate TLB
> > page sizes.
> 
> with something more like:
> 
> This enables PERF_SAMPLE_{DATA,CODE}_PAGE_SIZE to report accurate page
> table mapping sizes.

Sure.