linux-kernel - Re: [PATCH 1/2] kthread: convert worker lock to raw spinlock

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Message-ID: <20190213121301.d6sff2thya5eubwl@pathway.suse.cz>
Date:   Wed, 13 Feb 2019 13:13:01 +0100
From:   Petr Mladek <pmladek@...e.com>
To:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:     linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...nel.org>,
        tglx@...utronix.de, Julia Cartwright <julia@...com>,
        Guenter Roeck <linux@...ck-us.net>,
        Steffen Trumtrar <s.trumtrar@...gutronix.de>,
        Tim Sander <tim@...eglstein.org>
Subject: Re: [PATCH 1/2] kthread: convert worker lock to raw spinlock

On Tue 2019-02-12 17:25:53, Sebastian Andrzej Siewior wrote:
> From: Julia Cartwright <julia@...com>
> 
> In order to enable the queuing of kthread work items from hardirq
> context even when PREEMPT_RT_FULL is enabled, convert the worker
> spin_lock to a raw_spin_lock.
> 
> This is only acceptable to do because the work performed under the lock
> is well-bounded and minimal.

I could confirm that it is well-bounded and minimal. The most
expensive function probably is add_timer() called from
__kthread_queue_delayed_work(). It might spin a bit
to get timer->base->lock.

> Cc: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
> Cc: Guenter Roeck <linux@...ck-us.net>
> Reported-and-tested-by: Steffen Trumtrar <s.trumtrar@...gutronix.de>
> Reported-by: Tim Sander <tim@...eglstein.org>
> Signed-off-by: Julia Cartwright <julia@...com>
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>

Reviewed-by: Petr Mladek <pmladek@...e.com>

Best Regards,
Petr