From: Peter Williams <pwil3058@bigpond.net.au>
To: Ingo Molnar <mingo@elte.hu>
Cc: Darren Hart <darren@dvhart.com>,
linux-kernel@vger.kernel.org,
Thomas Gleixner <tglx@linutronix.de>,
"Stultz, John" <johnstul@us.ibm.com>,
"Siddha, Suresh B" <suresh.b.siddha@intel.com>,
Nick Piggin <nickpiggin@yahoo.com.au>
Subject: Re: RT task scheduling
Date: Sat, 08 Apr 2006 10:11:04 +1000 [thread overview]
Message-ID: <4436FF98.3050604@bigpond.net.au> (raw)
In-Reply-To: <20060406073753.GA18349@elte.hu>
Ingo Molnar wrote:
> * Darren Hart <darren@dvhart.com> wrote:
>
>> My last mail specifically addresses preempt-rt, but I'd like to know
>> people's thoughts regarding this issue in the mainline kernel. Please
>> see my previous post "realtime-preempt scheduling - rt_overload
>> behavior" for a testcase that produces unpredictable scheduling
>> results.
>
> the rt_overload feature i intend to push upstream-wards too, i just
> didnt separate it out of -rt yet.
>
> "RT overload scheduling" is a totally orthogonal mechanism to the SMP
> load-balancer (and this includes smpnice too) that is more or less
> equivalent to having a 'global runqueue' for real-time tasks, without
> the SMP overhead associated with that. If there is no "RT overload" [the
> common case even on Linux systems that _do_ make use of RT tasks
> occasionally], the new mechanism is totally inactive and there's no
> overhead. But once there are more RT tasks than CPUs, the scheduler will
> do "global" decisions for what RT tasks to run on which CPU.
Is this good enough? Isn't it possible with the current
try_to_wake_up() implementation (with or without smpnice) for two RT
tasks to end up on the same CPU even when there are less RT tasks than CPUs?
> To put even
> less overhead on the mainstream kernel, i plan to introduce a new
> SCHED_FIFO_GLOBAL scheduling policy to trigger this behavior. [it doesnt
> make much sense to extend SCHED_RR in that direction.]
I wouldn't have thought a new policy was necessary. Why not just do
this for all SCHED_FIFO (or even all RT) tasks?
BTW Does any body in the real world actually use SCHED_RR?
Peter
--
Peter Williams pwil3058@bigpond.net.au
"Learning, n. The kind of ignorance distinguishing the studious."
-- Ambrose Bierce
next prev parent reply other threads:[~2006-04-08 0:11 UTC|newest]
Thread overview: 37+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-04-06 3:25 RT task scheduling Darren Hart
2006-04-06 4:19 ` Peter Williams
2006-04-06 17:24 ` Darren Hart
2006-04-06 23:02 ` Peter Williams
2006-04-06 7:37 ` Ingo Molnar
2006-04-06 14:55 ` Darren Hart
2006-04-06 18:16 ` Darren Hart
2006-04-06 22:35 ` Darren Hart
2006-04-07 22:58 ` Vernon Mauery
2006-04-06 23:06 ` Peter Williams
2006-04-07 3:07 ` Bill Huey
2006-04-07 7:11 ` Ingo Molnar
2006-04-07 8:39 ` Bill Huey
2006-04-07 9:11 ` Bill Huey
2006-04-07 9:19 ` Ingo Molnar
2006-04-07 10:39 ` Bill Huey
2006-04-07 10:51 ` Ingo Molnar
2006-04-07 11:14 ` Bill Huey
2006-04-07 11:29 ` Ingo Molnar
2006-04-07 22:18 ` Bill Huey
2006-04-07 14:56 ` Darren Hart
2006-04-07 21:06 ` Bill Huey
2006-04-07 22:37 ` Darren Hart
2006-04-07 23:36 ` Bill Huey
2006-04-08 3:01 ` Steven Rostedt
2006-04-08 4:28 ` Vernon Mauery
2006-04-08 4:45 ` Steven Rostedt
2006-04-08 7:16 ` Ingo Molnar
2006-04-08 7:25 ` Ingo Molnar
2006-04-08 7:54 ` Bill Huey
2006-04-08 8:03 ` Ingo Molnar
2006-04-08 10:02 ` Bill Huey
2006-04-08 0:11 ` Peter Williams [this message]
2006-04-07 9:23 ` Bill Huey
2006-04-09 13:16 ` Ingo Molnar
2006-04-09 17:25 ` Darren Hart
2006-04-09 18:31 ` Ingo Molnar
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