linux-kernel - Re: [PATCH v10 00/25] Speculative page faults

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Message-ID: <87bmdynnv4.fsf@e105922-lin.cambridge.arm.com>
Date:   Wed, 02 May 2018 15:17:19 +0100
From:   Punit Agrawal <punit.agrawal@....com>
To:     Laurent Dufour <ldufour@...ux.vnet.ibm.com>
Cc:     akpm@...ux-foundation.org, mhocko@...nel.org, peterz@...radead.org,
        kirill@...temov.name, ak@...ux.intel.com, dave@...olabs.net,
        jack@...e.cz, Matthew Wilcox <willy@...radead.org>,
        benh@...nel.crashing.org, mpe@...erman.id.au, paulus@...ba.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, hpa@...or.com,
        Will Deacon <will.deacon@....com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>,
        kemi.wang@...el.com, sergey.senozhatsky.work@...il.com,
        Daniel Jordan <daniel.m.jordan@...cle.com>,
        David Rientjes <rientjes@...gle.com>,
        Jerome Glisse <jglisse@...hat.com>,
        Ganesh Mahendran <opensource.ganesh@...il.com>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        haren@...ux.vnet.ibm.com, khandual@...ux.vnet.ibm.com,
        npiggin@...il.com, bsingharora@...il.com,
        paulmck@...ux.vnet.ibm.com, Tim Chen <tim.c.chen@...ux.intel.com>,
        linuxppc-dev@...ts.ozlabs.org, x86@...nel.org
Subject: Re: [PATCH v10 00/25] Speculative page faults

Hi Laurent,

One query below -

Laurent Dufour <ldufour@...ux.vnet.ibm.com> writes:

[...]

>
> Ebizzy:
> -------
> The test is counting the number of records per second it can manage, the
> higher is the best. I run it like this 'ebizzy -mTRp'. To get consistent
> result I repeated the test 100 times and measure the average result. The
> number is the record processes per second, the higher is the best.
>
>   		BASE		SPF		delta	
> 16 CPUs x86 VM	12405.52	91104.52	634.39%
> 80 CPUs P8 node 37880.01	76201.05	101.16%

How do you measure the number of records processed? Is there a specific
version of ebizzy that reports this? I couldn't find a way to get this
information with the ebizzy that's included in ltp.

>
> Here are the performance counter read during a run on a 16 CPUs x86 VM:
>  Performance counter stats for './ebizzy -mRTp':
>             860074      faults
>             856866      spf
>                285      pagefault:spf_pte_lock
>               1506      pagefault:spf_vma_changed
>                  0      pagefault:spf_vma_noanon
>                 73      pagefault:spf_vma_notsup
>                  0      pagefault:spf_vma_access
>                  0      pagefault:spf_pmd_changed
>
> And the ones captured during a run on a 80 CPUs Power node:
>  Performance counter stats for './ebizzy -mRTp':
>             722695      faults
>             699402      spf
>              16048      pagefault:spf_pte_lock
>               6838      pagefault:spf_vma_changed
>                  0      pagefault:spf_vma_noanon
>                277      pagefault:spf_vma_notsup
>                  0      pagefault:spf_vma_access
>                  0      pagefault:spf_pmd_changed
>
> In ebizzy's case most of the page fault were handled in a speculative way,
> leading the ebizzy performance boost.

A trial run showed increased fault handling when SPF is enabled on an
8-core ARM64 system running 4.17-rc3. I am using a port of your x86
patch to enable spf on arm64.

SPF
---

Performance counter stats for './ebizzy -vvvmTRp':

         1,322,736      faults                                                      
         1,299,241      software/config=11/                                         

      10.005348034 seconds time elapsed

No SPF
-----

 Performance counter stats for './ebizzy -vvvmTRp':

           708,916      faults
                 0      software/config=11/

      10.005807432 seconds time elapsed

Thanks,
Punit

[...]