Re: [PATCH v3] scheduler: enhancement to show_state_filter and SysRq

[Peter Zijlstra]

On Wed, Aug 09, 2017 at 04:01:49PM +0800, Yafang Shao wrote:
> 2017-08-09 15:43 GMT+08:00 Peter Zijlstra <peterz@xxxxxxxxxxxxx>:
> > 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

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.