linux-kernel - Re: [PATCH 1/1] hung_task debugging: Add tracepoint to report the hang

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Message-ID: <20131029191016.GB27834@redhat.com>
Date:	Tue, 29 Oct 2013 20:10:16 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Dave Sullivan <dsulliva@...hat.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] hung_task debugging: Add tracepoint to report the
	hang

On 10/20, Ingo Molnar wrote:
>
> * Oleg Nesterov <oleg@...hat.com> wrote:
>
> > Currently check_hung_task() prints a warning if it detects the problem,
> > but it is not convenient to watch the system logs if user-space wants to
> > be notified about the hang.
> >
> > Add the new trace_sched_process_hang() into check_hung_task(), this way
> > a user-space monitor can easily wait for the hang and potentially
> > resolve a problem.
>
> I'm wondering, is the data of trace_console() in kernel/printk/printk.c
> not sufficient?

Probably yes... I do not think they disable CONFIG_PRINTK.

But this is obviously much less convenient, they will need to parse the
text. And the user-space watchdog will be woken up much more often than
necessary. And they could probably simply read /var/log or interact with
syslogd somehow, but they specially asked for something better and more
robust.

But of course, I understand that every tracepoint should be justified.
So if you do not like this change I try to convince them to use
trace_console().

> If it's not enough then it might be better to add a higher level printk
> tracepoint instead - that can catch hung_task messages and (much) more.

Not sure I understand... I mean I do not understand why this is really
better for them, except this will simplify the parsing a bit. Anyway
I'd prefer to not send another doubtful patch ;)

Thanks.

Oleg.

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