linux-kernel - Re: [PATCH v3] scheduler: enhancement to show_state

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Message-ID: <20170809074337.awcwac6u2cxr5h2m@hirez.programming.kicks-ass.net>
Date:   Wed, 9 Aug 2017 09:43:37 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Yafang Shao <laoar.shao@...il.com>
Cc:     mingo@...hat.com, gregkh@...uxfoundation.org, jslaby@...e.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] scheduler: enhancement to show_state_filter and SysRq

On Wed, Aug 09, 2017 at 06:31:28PM +0800, Yafang Shao wrote:
> Sometimes we want to get tasks in TASK_RUNNING sepcifically,
> instead of dump all tasks.
> 
> For example, when the loadavg are high, we want to dump
> tasks in TASK_RUNNING and TASK_UNINTERRUPTIBLE, which contribute
> to system load. But mostly there're lots of tasks in Sleep state,
> which occupies almost all of the kernel log buffer, even overflows
> it, that causes the useful messages get lost. Although we can
> enlarge the kernel log buffer, but that's not a good idea.

That's what you have serial consoles for...

> +static void sysrq_handle_showstate_load(int key)
>  {
> +	show_state_filter(TASK_UNINTERRUPTIBLE << 1 | (TASK_RUNNING | 0x1));
>  }

How is that not unreadable gunk?

> @@ -477,7 +478,7 @@ static void sysrq_handle_unrt(int key)
>  	&sysrq_mountro_op,		/* u */
>  	/* v: May be registered for frame buffer console restore */
>  	NULL,				/* v */
> -	&sysrq_showstate_blocked_op,	/* w */
> +	&sysrq_showstate_load_op,	/* w */
>  	/* x: May be registered on mips for TLB dump */
>  	/* x: May be registered on ppc/powerpc for xmon */
>  	/* x: May be registered on sparc64 for global PMU dump */

So I'm really not convinced this is useful. The blocked thing is very
useful if you're trying to debug a deadlock. Now you get endless clutter
with runnable tasks.

High load-avg as such isn't a problem. Why do you care?