linux-kernel - Re: Sending some form of notifaction when sched

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <AANLkTinch3-FHaOKTnfYnFLnG5uyRNfmpZP=RpLzJOrf@mail.gmail.com>
Date:	Mon, 27 Dec 2010 12:13:42 +0530
From:	Bharata B Rao <bharata.rao@...il.com>
To:	Dario Faggioli <raistlin@...ux.it>
Cc:	torbenh <torbenh@....de>, linux-kernel@...r.kernel.org,
	Peter Zijlstra <peterz@...radead.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...e.hu>,
	Gregory Haskins <ghaskins@...ell.com>,
	Nick Piggin <nickpiggin@...oo.com.au>
Subject: Re: Sending some form of notifaction when sched_fifo throttling kicks in...

On Thu, Dec 23, 2010 at 6:47 PM, Dario Faggioli <raistlin@...ux.it> wrote:
> On Thu, 2010-12-23 at 12:39 +0100, torbenh wrote:
>> hi...
>>
> Hi,
>
>> when the rt_runtime budget is exceeded, the kernel silently stops
>> scheduling RT tasks. there is no way to distinguish this from
>> a task taking very long to complete.
>>
> Well, this depends on how you do the accounting in your (user-level)
> code.
>
>> it would be very nice, if the kernel would send some form of notifaction
>> when it starts throttling things.
>>
> This might be tricky, if the meaning is signals or something to the
> throttled tasks, since you can have a (or more!) runqueue full of
> them... Are we signalling them all? Moreover, they'll get the
> notification only after resuming, and it's not guaranteed that this
> helps in finding out who is "responsible for" the throttling and... By
> the way...
>
>> recording the timestamp of the last occurence of throttling
>> in a /proc file would be sufficient, if there were no cgroups.
>>
>> would it be possible to add a readonly property to the cpu subsystem ?
>>
> ... If you think you're fine with some /proc (and perhaps cpuacct, if
> cgroups are being used) readable, I can try to come up with something.
>
> I think that the number of times that throttling fired and the last
> throttling instant could be exported this way without much issues.
>
> Do others have some idea and/or comments about that? This is
> ABI/interface, and that really scares me! :-P

You might want to note that CFS bandwidth control patches export some
such stats via a new per-cgroup file cpu.stat. It exports 3 statistics:

nr_periods: Number of enforcement intervals that have elapsed.
nr_throttled: Number of times the group has been throttled/limited.
throttled_time: The total time duration (in nanoseconds) for which the group
remained throttled.

Regards,
Bharata.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/