linux-kernel - Re: [PATCH v3 00/14] perf/hw_breakpoint: Optimize for thousands of tasks

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Date:   Tue, 16 Aug 2022 16:12:10 +0200
From:   Marco Elver <elver@...gle.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Ian Rogers <irogers@...gle.com>,
        Frederic Weisbecker <frederic@...nel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        linuxppc-dev@...ts.ozlabs.org, linux-perf-users@...r.kernel.org,
        x86@...nel.org, linux-sh@...r.kernel.org,
        kasan-dev@...glegroups.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 00/14] perf/hw_breakpoint: Optimize for thousands of tasks

On Wed, 20 Jul 2022 at 17:47, Ian Rogers <irogers@...gle.com> wrote:
> On Tue, Jul 12, 2022 at 6:41 AM Marco Elver <elver@...gle.com> wrote:
> > On Mon, 4 Jul 2022 at 17:05, Marco Elver <elver@...gle.com> wrote:
> > > The hw_breakpoint subsystem's code has seen little change in over 10
> > > years. In that time, systems with >100s of CPUs have become common,
> > > along with improvements to the perf subsystem: using breakpoints on
> > > thousands of concurrent tasks should be a supported usecase.
> > [...]
> > > Marco Elver (14):
> > >   perf/hw_breakpoint: Add KUnit test for constraints accounting
> > >   perf/hw_breakpoint: Provide hw_breakpoint_is_used() and use in test
> > >   perf/hw_breakpoint: Clean up headers
> > >   perf/hw_breakpoint: Optimize list of per-task breakpoints
> > >   perf/hw_breakpoint: Mark data __ro_after_init
> > >   perf/hw_breakpoint: Optimize constant number of breakpoint slots
> > >   perf/hw_breakpoint: Make hw_breakpoint_weight() inlinable
> > >   perf/hw_breakpoint: Remove useless code related to flexible
> > >     breakpoints
> > >   powerpc/hw_breakpoint: Avoid relying on caller synchronization
> > >   locking/percpu-rwsem: Add percpu_is_write_locked() and
> > >     percpu_is_read_locked()
> > >   perf/hw_breakpoint: Reduce contention with large number of tasks
> > >   perf/hw_breakpoint: Introduce bp_slots_histogram
> > >   perf/hw_breakpoint: Optimize max_bp_pinned_slots() for CPU-independent
> > >     task targets
> > >   perf/hw_breakpoint: Optimize toggle_bp_slot() for CPU-independent task
> > >     targets
> > [...]
> >
> > This is ready from our side, and given the silence, assume it's ready
> > to pick up and/or have a maintainer take a look. Since this is mostly
> > kernel/events, would -tip/perf/core be appropriate?
>
> These are awesome improvements, I've added my acked-by to every
> change. I hope we can pull these changes, as you say, into tip.git
> perf/core and get them into 5.20.

These still apply cleanly to 6.0-rc1 and the test passes, but let me
know if I shall send a rebased version.

Thanks
-- Marco