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

From: Punit Agrawal <punit.agrawal@arm.com>
To: Laurent Dufour <ldufour@linux.vnet.ibm.com>
Cc: akpm@linux-foundation.org, mhocko@kernel.org,
	peterz@infradead.org, kirill@shutemov.name, ak@linux.intel.com,
	dave@stgolabs.net, jack@suse.cz,
	Matthew Wilcox <willy@infradead.org>,
	benh@kernel.crashing.org, mpe@ellerman.id.au, paulus@samba.org,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>,
	hpa@zytor.com, Will Deacon <will.deacon@arm.com>,
	Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
	Andrea Arcangeli <aarcange@redhat.com>,
	Alexei Starovoitov <alexei.starovoitov@gmail.com>,
	kemi.wang@intel.com, sergey.senozhatsky.work@gmail.com,
	Daniel Jordan <daniel.m.jordan@oracle.com>,
	David Rientjes <rientjes@google.com>,
	Jerome Glisse <jglisse@redhat.com>,
	Ganesh Mahendran <opensource.ganesh@gmail.com>,
	linux-kernel@vger.kernel.org, linux-mm@kvack.org,
	haren@linux.vnet.ibm.com, khandual@linux.vnet.ibm.com,
	npiggin@gmail.com, bsingharora@gmail.com,
	paulmck@linux.vnet.ibm.com, Tim Chen <tim.c.chen@linux.intel.com>,
	linuxppc-dev@lists.ozlabs.org, x86@kernel.org
Subject: Re: [PATCH v10 00/25] Speculative page faults
Date: Wed, 02 May 2018 15:17:19 +0100	[thread overview]
Message-ID: <87bmdynnv4.fsf@e105922-lin.cambridge.arm.com> (raw)
In-Reply-To: <1523975611-15978-1-git-send-email-ldufour@linux.vnet.ibm.com> (Laurent Dufour's message of "Tue, 17 Apr 2018 16:33:06 +0200")

Hi Laurent,

One query below -

Laurent Dufour <ldufour@linux.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

[...]