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

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Date:   Mon, 25 Nov 2019 14:27:20 +0300
From:   Alexey Budankov <alexey.budankov@...ux.intel.com>
To:     Jiri Olsa <jolsa@...hat.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 25.11.2019 14:21, Jiri Olsa wrote:
> 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

If vfprintf() explicitly terminates output buffer with zero then
the initialization above can be avoided.

> 
> jirka
> 

~Alexey