linux-kernel - Re: periods and deadlines in 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: <FAC10E24-7049-4C2C-8B54-DB0EDF1D449E@cs.unc.edu>
Date:	Wed, 4 Aug 2010 01:02:41 -0400
From:	Bjoern Brandenburg <bbb@...unc.edu>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Bjoern Brandenburg <bbb@...il.unc.edu>,
	Raistlin <raistlin@...ux.it>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Song Yuan <song.yuan@...csson.com>,
	Dmitry Adamushko <dmitry.adamushko@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Nicola Manica <nicola.manica@...i.unitn.it>,
	Luca Abeni <lucabe72@...il.it>,
	Claudio Scordino <claudio@...dence.eu.com>,
	Harald Gustafsson <harald.gustafsson@...csson.com>,
	"bastoni@...unc.edu" <bastoni@...unc.edu>,
	Giuseppe Lipari <lipari@...is.sssup.it>
Subject: Re: periods and deadlines in SCHED_DEADLINE

On Aug 3, 2010, at 5:46 AM, Peter Zijlstra <peterz@...radead.org> wrote:

> On Sun, 2010-07-11 at 08:42 +0200, Bjoern Brandenburg wrote:
>> If you want to do G-EDF with limited and different budgets on each CPU
>> (e.g., G-EDF tasks may only run for 100 out of 1000 ms on CPU 0, but
>> for 400 out of 1000 ms on CPU 1), then you are entering the domain of
>> restricted-supply scheduling, which is significantly more complicated
>> to analyze (see [1,2]).
> 
> Would making the thing homogenious by assuming the worst for all cpus
> make the analysis easier? That is, in the above example, only allow the
> G-EDF scheduler to run for 100 out of 1000 ms on both cpus.

It would, but that severely limits your non-G-EDF tasks. What if you want to provision a P-EDF task with a period of ten milliseconds? If you allow a G-EDF slice of guaranteed 100 ms, then your P-EDF task might miss a deadline if it arrives at the wrong time. If you let it preempt the G-EDF slice, then you get "out of sync" and the analysis can become tricky. If you scale down the G-EDF time slice length to less than ten ms, then overheads increase needlessly on all processors. EDF-HSB addresses specifically this problem (for the case where G-EDF is only used for soft tasks):

B. Brandenburg and J. Anderson, “Integrating Hard/Soft Real-Time Tasks and Best-Effort Jobs on Multiprocessors”, Proceedings of the 19th Euromicro Conference on Real-Time Systems (ECRTS 2007), pp. 61-70. IEEE, July 2007. http://www.cs.unc.edu/~anderson/papers/ecrts07b.pdf

- Björn--
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/