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

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Message-ID: <CALOAHbDJ_zsUzFzSLSjRbQoi3ko7i2P2fPDFT4zdrkD=pBZg3g@mail.gmail.com>
Date:   Wed, 9 Aug 2017 17:26:14 +0800
From:   Yafang Shao <laoar.shao@...il.com>
To:     Peter Zijlstra <peterz@...radead.org>
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

2017-08-09 17:09 GMT+08:00 Peter Zijlstra <peterz@...radead.org>:
> On Wed, Aug 09, 2017 at 04:01:49PM +0800, Yafang Shao wrote:
>> 2017-08-09 15:43 GMT+08:00 Peter Zijlstra <peterz@...radead.org>:
>> > 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...
>> >
>> mostly we don't even have one console because we alwayas login the
>> servers via ssh. And manage the servers with console is not so convenient.
>
> I find IPMI SOL very useful. Serial console (esp. earlyprintk) keeps on
> working long after most other things have died.
>
> In any case, you can easily dump the printk output into your ssh session
> if you want, use something like:
>
>         cat /dev/kmsg | tee logfile & echo t > /proc/sysrq-trigger

that's what I'm doing it currently :)
Then I thought deeply why not do it more smartly?
Introducing a new key(here I just modified the key 'w') only dump
tasks in running and blocked should be more smarter.

>
> I really see no problem here. Then you can run a bit of awk or whatever
> your favourite tool is to filter out the stuff you don't want.
>
Another question, if we could filter with scritpts in userland, why
did we introduced the key 'w' to dump only blocked state
as we already have a key 't' to dump all tasks ?

Thanks
Yafang