linux-kernel - Re: [PATCH] arc: perf: Enable generic "cache-references" and "cache-misses" events

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Date:   Wed, 31 Aug 2016 12:05:14 -0700
From:   Vineet Gupta <Vineet.Gupta1@...opsys.com>
To:     Peter Zijlstra <a.p.zijlstra@...llo.nl>,
        Jiri Olsa <jolsa@...hat.com>
CC:     Alexey Brodkin <Alexey.Brodkin@...opsys.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Arnaldo Carvalho de Melo" <acme@...hat.com>,
        "linux-snps-arc@...ts.infradead.org" 
        <linux-snps-arc@...ts.infradead.org>,
        "linux-perf-users@...r.kernel.org" <linux-perf-users@...r.kernel.org>,
        Will Deacon <Will.Deacon@....com>
Subject: Re: [PATCH] arc: perf: Enable generic "cache-references" and
 "cache-misses" events

On 08/26/2016 10:31 AM, Vineet Gupta wrote:
> On 08/25/2016 04:49 AM, Alexey Brodkin wrote:
>> ...
>>  	[PERF_COUNT_ARC_EDTLB] = "edtlb",	/* D-TLB Miss */
>>  	[PERF_COUNT_ARC_EITLB] = "eitlb",	/* I-TLB Miss */
>> +
>> +	[PERF_COUNT_HW_CACHE_REFERENCES] = "imemrdc",	/* Instr: mem read cached */
>> +	[PERF_COUNT_HW_CACHE_MISSES] = "dclm",		/* D-cache Load Miss */
> I think this is duplicating a mistake we already have. I vaguely remember when
> doing some hackbench profiling last year with range based profiling confined to
> memset routine and saw that L1-dcache-misses was counting zero. This is because it
> only counts LD misses while memset only does ST.
>
> Performance counter stats for '/sbin/hackbench':
>
>      0 L1-dcache-misses
>      0 L1-dcache-load-misses
>      1846082 L1-dcache-store-misses
>
>
> @PeterZ do you concur that is wrong and we ought to setup 2 counters to do this
> correctly ?

Hi Peter / Will,

Can you provide some guidance here. So I looked at what others do -
ARMV7_PERFCTR_L1_DCACHE_REFILL counts both load and store misses, while ARC has 2
separate conditions for load or stores. Is there an existing mechanism to "group"
/ "add" them to give a cumulative PERF_COUNT_HW_CACHE_MISSES - is that what perf
event grouping is ?

Quoting from perf wiki @ https://perf.wiki.kernel.org/index.php/Tutorial

"It can be interesting to try and pack events in a way that guarantees that event
A and B are always measured together. Although the perf_events kernel interface
provides support for event grouping, the current perf tool does *not*."

Thx,
-Vineet