linux-kernel - Re: [PATCH] sched/rt: fix rt timer activation/deactivation

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Date:	Wed, 26 Feb 2014 13:35:42 +0400
From:	Kirill Tkhai <tkhai@...dex.ru>
To:	Peter Zijlstra <peterz@...radead.org>,
	Mike Galbraith <bitbucket@...ine.de>
Cc:	Juri Lelli <juri.lelli@...il.com>,
	"mingo@...hat.com" <mingo@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] sched/rt: fix rt timer activation/deactivation



26.02.2014, 13:07, "Peter Zijlstra" <peterz@...radead.org>:
> On Wed, Feb 26, 2014 at 03:37:38AM +0100, Mike Galbraith wrote:
>
>>  BTW, I noticed you can no longer turn the turn the noisy thing off since
>>  we grew DL.  I added an old SGI boot parameter to tell it to go away.
>
> You're talking about the rt badnwidth timer, right?
>
>  1) why won't it go away with DL added?

We know nothing about rt_time and rt_runtime values, when we are doing
update_curr_dl().

rt_time maybe not zero, so we increment rt_time.

rt_rq->rt_runtime maybe less than maximum available for RT(and for dl too),
because someone could borrow a part of rt_runtime during previous
balance_runtime().

If dl task uses all available runtime, we always will have "idle = 0"

        if (rt_rq->rt_time || rt_rq->rt_nr_running)
                idle = 0;

in do_sched_rt_period_timer(). Timer will be restarted.

This is boundary case, of course.

>  2) it should never appear when !rt_bandwidth_enabled(), so if you set
>  sysctl_sched_rt_runtime to -1 all this should go away already, no extra
>  patches required.
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