Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
MIME-Version: 1.0
References: <20220628095833.2579903-1-elver@google.com> <20220628095833.2579903-9-elver@google.com>
 <045a825c-cd7d-5878-d655-3d55fffb9ac2@csgroup.eu>
In-Reply-To: <045a825c-cd7d-5878-d655-3d55fffb9ac2@csgroup.eu>
From:   Marco Elver <elver@google.com>
Date:   Fri, 1 Jul 2022 11:41:25 +0200
Message-ID: <CANpmjNOeyZ0MZ_esOnR7TUE1R5Vf+_Ejt5JRQ1AoAmhkCrVrBA@mail.gmail.com>
Subject: Re: [PATCH v2 08/13] powerpc/hw_breakpoint: Avoid relying on caller synchronization
To:     Christophe Leroy <christophe.leroy@csgroup.eu>
Cc:     Peter Zijlstra <peterz@infradead.org>,
        Frederic Weisbecker <frederic@kernel.org>,
        Ingo Molnar <mingo@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        "linux-sh@vger.kernel.org" <linux-sh@vger.kernel.org>,
        Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        "x86@kernel.org" <x86@kernel.org>,
        "linuxppc-dev@lists.ozlabs.org" <linuxppc-dev@lists.ozlabs.org>,
        Arnaldo Carvalho de Melo <acme@kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linux-perf-users@vger.kernel.org" <linux-perf-users@vger.kernel.org>,
        "kasan-dev@googlegroups.com" <kasan-dev@googlegroups.com>,
        Namhyung Kim <namhyung@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Jiri Olsa <jolsa@redhat.com>,
        Dmitry Vyukov <dvyukov@google.com>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
Precedence: bulk

On Fri, 1 Jul 2022 at 10:54, Christophe Leroy
<christophe.leroy@csgroup.eu> wrote:
>
> Hi Marco,
>
> Le 28/06/2022 =C3=A0 11:58, Marco Elver a =C3=A9crit :
> > Internal data structures (cpu_bps, task_bps) of powerpc's hw_breakpoint
> > implementation have relied on nr_bp_mutex serializing access to them.
> >
> > Before overhauling synchronization of kernel/events/hw_breakpoint.c,
> > introduce 2 spinlocks to synchronize cpu_bps and task_bps respectively,
> > thus avoiding reliance on callers synchronizing powerpc's hw_breakpoint=
.
>
> We have an still opened old issue in our database related to
> hw_breakpoint, I was wondering if it could have any link with the
> changes you are doing and whether you could handle it at the same time.
>
> https://github.com/linuxppc/issues/issues/38
>
> Maybe it is completely unrelated, but as your series modifies only
> powerpc and as the issue says that powerpc is the only one to do that, I
> thought it might be worth a hand up.

I see the powerpc issue unrelated to the optimizations in this series;
perhaps by fixing the powerpc issue, it would also become more
optimal. But all I saw is that it just so happens that powerpc relied
on the nr_bp_mutex which is going away.

This series will become even more complex if I decided to add a
powerpc rework on top (notwithstanding the fact I don't have any ppc
hardware at my disposal either). A separate series/patch seems much
more appropriate.

Thanks,
-- Marco