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Date: Wed, 5 Mar 2014 12:59:42 +0100
From: Peter Zijlstra <peterz@infradead.org>
To: Kirill Tkhai <ktkhai@parallels.com>
Cc: linux-kernel@vger.kernel.org, Juri Lelli <juri.lelli@gmail.com>,
        Ingo Molnar <mingo@redhat.com>, tkhai@yandex.ru
Subject: Re: [PATCH tip] sched/rt: Fix picking RT and DL tasks from empty
 queue
Message-ID: <20140305115942.GX9987@twins.programming.kicks-ass.net>
References: <1393946746.3643.3.camel@tkhai>
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On Tue, Mar 04, 2014 at 07:25:46PM +0400, Kirill Tkhai wrote:
> The problems:
> 
> 1)We check for rt_nr_running before call of put_prev_task().
> If previous task is RT, its rt_rq may become throttled
> and dequeued after this call.
> 
> In case of p is from rt->rq this just causes picking a task
> from throttled queue, but in case of its rt_rq is child
> we are guaranteed catch BUG_ON.
>     
> 2)The same with deadline class. The only difference we operate
> on only dl_rq.
>     
> This patch fix all above and it adds a small skip in DL update
> like we've already done for RT class:
> 
> 	if (unlikely((s64)delta_exec <= 0))
> 		return;
> 
> This will optimize sequential update_curr_dl() calls a little.
> 

Ah indeed, good catch that. Thanks!