linux-kernel - Re: [PATCH v3 3/4] perf record: apply affinity masks when reading mmap buffers

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Date:   Thu, 10 Jan 2019 12:41:55 +0300
From:   Alexey Budankov <alexey.budankov@...ux.intel.com>
To:     Jiri Olsa <jolsa@...hat.com>
Cc:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Andi Kleen <ak@...ux.intel.com>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 3/4] perf record: apply affinity masks when reading
 mmap buffers

On 09.01.2019 19:53, Jiri Olsa wrote:
> On Wed, Jan 09, 2019 at 12:38:23PM +0300, Alexey Budankov wrote:
> 
> SNIP
> 
>> diff --git a/tools/perf/util/mmap.c b/tools/perf/util/mmap.c
>> index e5220790f1fb..ee0230eed635 100644
>> --- a/tools/perf/util/mmap.c
>> +++ b/tools/perf/util/mmap.c
>> @@ -377,6 +377,24 @@ void perf_mmap__munmap(struct perf_mmap *map)
>>  	auxtrace_mmap__munmap(&map->auxtrace_mmap);
>>  }
>>  
>> +static void perf_mmap__setup_affinity_mask(struct perf_mmap *map, struct mmap_params *mp)
>> +{
>> +	int c, cpu, nr_cpus, node;
>> +
>> +	CPU_ZERO(&map->affinity_mask);
>> +	if (mp->affinity == PERF_AFFINITY_NODE && cpu__max_node() > 1) {
>> +		nr_cpus = cpu_map__nr(mp->cpu_map);
>> +		node = cpu__get_node(map->cpu);
>> +		for (c = 0; c < nr_cpus; c++) {
>> +			cpu = mp->cpu_map->map[c]; /* map c index to online cpu index */
>> +			if (cpu__get_node(cpu) == node)
>> +				CPU_SET(cpu, &map->affinity_mask);
> 
> should we do that from from all possible cpus task (perf record)
> can run on, instead of mp->cpu_map, which might be only subset
> (-C ... option)

That is how it should be and because mp->cpu_map depends on -C option value 
in this patch set version it requires to be corrected, possibly like this:

struct mmap_params mp = {
		.nr_cblocks	= nr_cblocks,
		.affinity	= affinity,
		.cpu_map	= cpu_map__new(NULL) /* builds struct cpu_map from /sys/devices/system/cpu/online */
	}; 
and 
	if (mp->affinity == PERF_AFFINITY_NODE && cpu__max_node() > 1 && mp->cpu_map)

Thanks!

> 
> also node -> cpu_map is static configuration, we could prepare
> this map ahead (like cpunode_map) and just assign it in here
> based on node index

It makes sense and either way is possible. However the static configuration 
looks a bit trickier because it incurs additional mask objects duplication 
and conversion from struct cpu_map to cpu_set_t still remains the same.

Thanks,
Alexey

> 
> thanks,
> jirka
>