linux-kernel - Re: [PATCH 13/16] perf: Add a speculative page fault sw events

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Date:   Wed, 9 Aug 2017 15:25:48 +0200
From:   Laurent Dufour <ldufour@...ux.vnet.ibm.com>
To:     Michael Ellerman <mpe@...erman.id.au>, paulmck@...ux.vnet.ibm.com,
        peterz@...radead.org, akpm@...ux-foundation.org,
        kirill@...temov.name, ak@...ux.intel.com, mhocko@...nel.org,
        dave@...olabs.net, jack@...e.cz,
        Matthew Wilcox <willy@...radead.org>, benh@...nel.crashing.org,
        paulus@...ba.org, Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, hpa@...or.com,
        Will Deacon <will.deacon@....com>
Cc:     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,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        linuxppc-dev@...ts.ozlabs.org, x86@...nel.org
Subject: Re: [PATCH 13/16] perf: Add a speculative page fault sw events

On 09/08/2017 15:18, Michael Ellerman wrote:
> Laurent Dufour <ldufour@...ux.vnet.ibm.com> writes:
> 
>> Add new software events to count succeeded and failed speculative page
>> faults.
>>
>> Signed-off-by: Laurent Dufour <ldufour@...ux.vnet.ibm.com>
>> ---
>>  include/uapi/linux/perf_event.h | 2 ++
>>  1 file changed, 2 insertions(+)
>>
>> diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h
>> index b1c0b187acfe..fbfb03dff334 100644
>> --- a/include/uapi/linux/perf_event.h
>> +++ b/include/uapi/linux/perf_event.h
>> @@ -111,6 +111,8 @@ enum perf_sw_ids {
>>  	PERF_COUNT_SW_EMULATION_FAULTS		= 8,
>>  	PERF_COUNT_SW_DUMMY			= 9,
>>  	PERF_COUNT_SW_BPF_OUTPUT		= 10,
>> +	PERF_COUNT_SW_SPF_DONE			= 11,
>> +	PERF_COUNT_SW_SPF_FAILED		= 12,
> 
> Can't you calculate:
> 
>   PERF_COUNT_SW_SPF_FAILED = PERF_COUNT_SW_PAGE_FAULTS - PERF_COUNT_SW_SPF_DONE
> 
> ie. do you need a separate event for it?

Unfortunately not, because PERF_COUNT_SW_PAGE_FAULTS counts also page
faults from the kernel space, while SPF is only concerning user space page
faults.

Cheers,
Laurent.