linux-kernel - Re: [RFC][PATCH 2/4] printk: offload printing from wake_up_klogd_work

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Date:   Thu, 23 Mar 2017 13:11:06 +0100
From:   Petr Mladek <pmladek@...e.com>
To:     Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        "Rafael J . Wysocki" <rjw@...ysocki.net>,
        linux-kernel@...r.kernel.org,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>
Subject: Re: [RFC][PATCH 2/4] printk: offload printing from
 wake_up_klogd_work_func()

On Thu 2017-03-23 18:00:42, Sergey Senozhatsky wrote:
> On (03/20/17 17:09), Petr Mladek wrote:
> [..]
> > 
> > BTW: wake_up_klogd_work does not need to be per-CPU as well.
> > irq_work infrastructure heavily uses per-CPU variables.
> > But a global struct irq_work is safe, see irq_work_claim().
> 
> so I have a patch that turns wake_up_klogd_work into a global variable,
> out of curiosity, but I'm not entire sure about it. the sort of a problem
> is that queued irq_works still go into a per-CPU run_lists.  per-CPU
> wake_up_klogd_work permits us to queue irq work on several CPUs so we
> might have better chances to execute wake_up_klogd_work_func(), while
> global wake_up_klogd_work will be only in one run_list. this can defer
> wake_up_klogd_work processing until that particular single CPU handles
> its interrupt and calls irq_work_run_list(). what do you think?

Good question! I personally think that it should not cause a big harm
but I am not completely sure. It might need some more testing.

Let's postpone this change and do it alone in the future.

Best Regards,
Petr