linux-kernel - Re: [PATCH 0/7] RT: (RFC) RT-Overload/Sched enhancements

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Date:	Fri, 12 Oct 2007 07:47:15 -0400 (EDT)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Peter Zijlstra <peterz@...radead.org>
cc:	Gregory Haskins <ghaskins@...ell.com>,
	linux-rt-users <linux-rt-users@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/7] RT: (RFC) RT-Overload/Sched enhancements


--

On Fri, 12 Oct 2007, Peter Zijlstra wrote:

>
> And for that, steve's rq->curr_prio field seems quite suitable.
>
> so instead of the:
>   for (3 tries)
>     find lowest cpu
>     try push
>
> we do:
>
>   cpu_hotplug_lock();
>   cpus_and(mask, p->cpus_allowed, online_cpus);
>   for_each_cpu_mask(i, mask) {
>     if (cpu_rq(i)->curr_prio > p->prio && push_task(p, i))
>       break;
>   }
>   cpu_hotplug_unlock();

The thing I'm worried about is that we pushed off a rt task that is higher
in prio than another rt task on another cpu, and we'll cause a bunch of
rt task bouncing.  That is what I'm trying to avoid.

BTW, my logging has showed that I have yet to hit a 2cd try (but I admit,
this is a very limited test set).

-- Steve
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