linux-kernel - Re: [PATCH v2 3/3] perf record: adapt affinity to machines with #CPUs

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Message-ID: <20191125112122.GA1201@krava>
Date:   Mon, 25 Nov 2019 12:21:22 +0100
From:   Jiri Olsa <jolsa@...hat.com>
To:     Alexey Budankov <alexey.budankov@...ux.intel.com>
Cc:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Andi Kleen <ak@...ux.intel.com>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 3/3] perf record: adapt affinity to machines with
 #CPUs > 1K

On Mon, Nov 25, 2019 at 02:13:20PM +0300, Alexey Budankov wrote:
> On 25.11.2019 12:42, Jiri Olsa wrote:
> > On Mon, Nov 25, 2019 at 09:08:57AM +0300, Alexey Budankov wrote:
> > 
> > SNIP
> > 
> >> -static void perf_mmap__setup_affinity_mask(struct mmap *map, struct mmap_params *mp)
> >> +static int perf_mmap__setup_affinity_mask(struct mmap *map, struct mmap_params *mp)
> >>  {
> >> -	CPU_ZERO(&map->affinity_mask);
> >> +	map->affinity_mask.nbits = cpu__max_cpu();
> >> +	map->affinity_mask.bits = bitmap_alloc(map->affinity_mask.nbits);
> >> +	if (!map->affinity_mask.bits)
> >> +		return -1;
> >> +
> >>  	if (mp->affinity == PERF_AFFINITY_NODE && cpu__max_node() > 1)
> >>  		build_node_mask(cpu__get_node(map->core.cpu), &map->affinity_mask);
> >>  	else if (mp->affinity == PERF_AFFINITY_CPU)
> >> -		CPU_SET(map->core.cpu, &map->affinity_mask);
> >> +		set_bit(map->core.cpu, map->affinity_mask.bits);
> >> +
> >> +	return 0;
> >>  }
> >>  
> >> +#define MASK_SIZE 1023
> >>  int mmap__mmap(struct mmap *map, struct mmap_params *mp, int fd, int cpu)
> >>  {
> >> +	char mask[MASK_SIZE + 1] = {0};
> > 
> > does this need to be initialized?
> 
> This is to make sure the message is zero terminated for vfprintf call()

hum AFAICS it's used only in bitmap_scnprintf, which should
terminate the string properly

jirka

> 
> > 
> >> +
> >>  	if (perf_mmap__mmap(&map->core, &mp->core, fd, cpu)) {
> >>  		pr_debug2("failed to mmap perf event ring buffer, error %d\n",
> >>  			  errno);
> >>  		return -1;
> >>  	}
> >>  
> >> -	perf_mmap__setup_affinity_mask(map, mp);
> >> +	if (perf_mmap__setup_affinity_mask(map, mp)) {
> >> +		pr_debug2("failed to alloc mmap affinity mask, error %d\n",
> >> +			  errno);
> >> +		return -1;
> >> +	}
> >> +	bitmap_scnprintf(map->affinity_mask.bits, map->affinity_mask.nbits, mask, MASK_SIZE);
> >> +	pr_debug2("%p: mmap mask[%ld]: %s\n", map, map->affinity_mask.nbits, mask);
> > 
> > the bitmap_scnprintf could be called only for debug case, right?
> 
> Right. It is required to prepare debug message.
> 
> > 
> > 	if (version >= 2) {
> > 		bitmap_scnprintf(map->affinity_mask.bits, map->affinity_mask.nbits, mask, MASK_SIZE);
> > 		pr_debug2("%p: mmap mask[%ld]: %s\n", map, map->affinity_mask.nbits, mask);
> > 	}
> > 
> > ditto int the record__adjust_affinity function
> > 
> > jirka
> > 
> > 
> 
> ~Alexey
>