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From:   Ian Rogers <irogers@google.com>
Date:   Wed, 20 Jul 2022 08:47:08 -0700
Message-ID: <CAP-5=fXgYWuHKkfAxxTeAzTuq7PLwMd6UvBu+J+6tnqHwraSCA@mail.gmail.com>
Subject: Re: [PATCH v3 00/14] perf/hw_breakpoint: Optimize for thousands of tasks
To:     Marco Elver <elver@google.com>
Cc:     Peter Zijlstra <peterz@infradead.org>,
        Frederic Weisbecker <frederic@kernel.org>,
        Ingo Molnar <mingo@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Arnaldo Carvalho de Melo <acme@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        Jiri Olsa <jolsa@redhat.com>,
        Namhyung Kim <namhyung@kernel.org>,
        Dmitry Vyukov <dvyukov@google.com>,
        Michael Ellerman <mpe@ellerman.id.au>,
        linuxppc-dev@lists.ozlabs.org, linux-perf-users@vger.kernel.org,
        x86@kernel.org, linux-sh@vger.kernel.org,
        kasan-dev@googlegroups.com, linux-kernel@vger.kernel.org
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On Tue, Jul 12, 2022 at 6:41 AM Marco Elver <elver@google.com> wrote:
>
> On Mon, 4 Jul 2022 at 17:05, Marco Elver <elver@google.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.

Thanks,
Ian

> Thanks,
> -- Marco