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

Andi Kleen
2019-10-23T17:19:09Z

On Wed, Oct 23, 2019 at 07:16:13PM +0300, Alexey Budankov wrote:
>
> 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.

What I meant the cpu_set usages you added in

commit 9d2ed64587c045304efe8872b0258c30803d370c
Author: Alexey Budankov <alexey.budankov@linux.intel.com>
Date: Tue Jan 22 20:47:43 2019 +0300

perf record: Allocate affinity masks

need to be fixed to allocate dynamically, or at least use MAX_NR_CPUs to
support systems with >1024CPUs. That's an independent functionality
problem.

I haven't seen any large enough perf record usage to run
into the IPI problems for record.

-Andi