linux-kernel - Re: [PATCH PREEMPT_RT] kcov: fix locking splat from kcov_remote

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Date:   Wed, 11 Aug 2021 14:25:29 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:     Clark Williams <williams@...hat.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Andrey Konovalov <andreyknvl@...il.com>,
        kasan-dev@...glegroups.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH PREEMPT_RT] kcov:  fix locking splat from
 kcov_remote_start()

On Wed, Aug 11 2021 at 11:00, Sebastian Andrzej Siewior wrote:
> On 2021-08-10 22:38:30 [+0200], Thomas Gleixner wrote:
>> And that matters because? kcov has a massive overhead and with that
>> enabled you care as much about latencies as you do when running with
>> lockdep enabled.
>
> I wasn't aware of that. However, with that local_irq_save() ->
> local_lock_irqsave() swap and that first C code from
> Documentation/dev-tools/kcov.rst I don't see any spike in cyclictest's
> results. Maybe I'm not using it right…

The problem starts with remote coverage AFAICT.