linux-kernel - Re: [PATCH v2 4/9] perf affinity: Add infrastructure to save/restore affinity

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Date:   Wed, 23 Oct 2019 19:16:13 +0300
From:   Alexey Budankov <alexey.budankov@...ux.intel.com>
To:     Andi Kleen <ak@...ux.intel.com>
Cc:     Jiri Olsa <jolsa@...hat.com>, Andi Kleen <andi@...stfloor.org>,
        acme@...nel.org, linux-kernel@...r.kernel.org, jolsa@...nel.org,
        eranian@...gle.com, kan.liang@...ux.intel.com, peterz@...radead.org
Subject: Re: [PATCH v2 4/9] perf affinity: Add infrastructure to save/restore
 affinity


On 23.10.2019 17:52, Andi Kleen wrote:
> On Wed, Oct 23, 2019 at 04:30:49PM +0200, Jiri Olsa wrote:
>> On Wed, Oct 23, 2019 at 06:02:35AM -0700, Andi Kleen wrote:
>>> On Wed, Oct 23, 2019 at 11:59:11AM +0200, Jiri Olsa wrote:
>>>> On Sun, Oct 20, 2019 at 10:51:57AM -0700, Andi Kleen wrote:
>>>>
>>>> SNIP
>>>>
>>>>> +}
>>>>> diff --git a/tools/perf/util/affinity.h b/tools/perf/util/affinity.h
>>>>> new file mode 100644
>>>>> index 000000000000..e56148607e33
>>>>> --- /dev/null
>>>>> +++ b/tools/perf/util/affinity.h
>>>>> @@ -0,0 +1,15 @@
>>>>> +// SPDX-License-Identifier: GPL-2.0
>>>>> +#ifndef AFFINITY_H
>>>>> +#define AFFINITY_H 1
>>>>> +
>>>>> +struct affinity {
>>>>> +	unsigned char *orig_cpus;
>>>>> +	unsigned char *sched_cpus;
>>>>
>>>> why not use cpu_set_t directly?
>>>
>>> Because it's too small in glibc (only 1024 CPUs) and perf already 
>>> supports more.
>>
>> nice, we're using it all over the place.. how about using bitmap_alloc?
> 
> Okay.
> 
> The other places is mainly perf record from Alexey's recent affinity changes.
> These probably need to be fixed.
> 
> +Alexey

Despite the issue indeed looks generic for stat and record modes,
have you already observed record startup overhead somewhere in your setups?
I would, first, prefer to reproduce the overhead, to have stable use case 
for evaluation and then, possibly, improvement.

~Alexey