Re: [RFC v5 5/9] sched/deadline: do not reclaim the whole CPU bandwidth

Path	csiph.com!1.us.feeder.erje.net!2.us.feeder.erje.net!feeder.erje.net!2.eu.feeder.erje.net!newsfeed.fsmpi.rwth-aachen.de!newsfeed.straub-nv.de!news.mixmin.net!aioe.org!bofh.it!news.nic.it!robomod
From	Peter Zijlstra <peterz@infradead.org>
Newsgroups	linux.kernel
Subject	Re: [RFC v5 5/9] sched/deadline: do not reclaim the whole CPU bandwidth
Date	Fri, 24 Mar 2017 15:10:02 +0100
Message-ID	<toy4G-2Fu-31@gated-at.bofh.it> (permalink)
References	<toh3P-72e-5@gated-at.bofh.it> <toh3P-72e-3@gated-at.bofh.it>
X-Original-To	luca abeni <luca.abeni@santannapisa.it>
Dkim-Signature	v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=merlin.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=qs5OzKw/VPNr8ax0vHVCs8wS0zZX4fIZMJgGFvnzuYA=; b=d1DY6E/svcPCazJZoVfhH//Pf bbjyBsVSdYcefy34CRtnw1KTMzfNQUxwaS1sl3ViLOWbzea3u2rTbU1cUyrkFIIJiwQvfuYHXRNQF zllNktz85F8cjzsbHcUuKJEv/oT/+kp4/Bty1IThUz6cYLHZFYw56TdVeujOGprLFOpF9toVRNQ43 OrBxkghij9OpSy5lAGycrSO9l+7Kj9XNsStaa3UA5u7d3clcVzR8mlNJMn4xDjZFZUtraOZLo8p8+ 8SymS2YVC42xG7rr4ontpE5fTpN/Gjs3EieOeXAweH6rjSgGAENk882w7778e3ePIcqwN/34MMaho m0TbVLrUg==;
MIME-Version	1.0
Content-Type	text/plain; charset=us-ascii
Content-Disposition	inline
User-Agent	NeoMutt/20170113 (1.7.2)
Sender	robomod@news.nic.it
List-ID	<linux-kernel.vger.kernel.org>
X-Mailing-List	linux-kernel@vger.kernel.org
Approved	robomod@news.nic.it
Lines	58
Organization	linux.* mail to news gateway
X-Original-Cc	linux-kernel@vger.kernel.org, Ingo Molnar <mingo@redhat.com>, Juri Lelli <juri.lelli@arm.com>, Claudio Scordino <claudio@evidence.eu.com>, Steven Rostedt <rostedt@goodmis.org>, Tommaso Cucinotta <tommaso.cucinotta@sssup.it>, Daniel Bristot de Oliveira <bristot@redhat.com>, Joel Fernandes <joelaf@google.com>, Mathieu Poirier <mathieu.poirier@linaro.org>
X-Original-Date	Fri, 24 Mar 2017 15:00:15 +0100
X-Original-Message-ID	<20170324140015.fptmmtqynvjy723q@hirez.programming.kicks-ass.net>
X-Original-References	<1490327582-4376-1-git-send-email-luca.abeni@santannapisa.it> <1490327582-4376-6-git-send-email-luca.abeni@santannapisa.it>
X-Original-Sender	linux-kernel-owner@vger.kernel.org
Xref	csiph.com linux.kernel:1608422

Show key headers only | View raw

On Fri, Mar 24, 2017 at 04:52:58AM +0100, luca abeni wrote:

> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 20c62e7..efa88eb 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -6716,6 +6716,12 @@ static void sched_dl_do_global(void)
>  		raw_spin_unlock_irqrestore(&dl_b->lock, flags);
>  
>  		rcu_read_unlock_sched();
> +		if (dl_b->bw == -1)
> +			cpu_rq(cpu)->dl.deadline_bw_inv = 1 << 8;
> +		else
> +			cpu_rq(cpu)->dl.deadline_bw_inv =
> +				to_ratio(global_rt_runtime(),
> +					 global_rt_period()) >> 12;

Coding style requires braces here (on both legs of the condition)..

Also, I find deadline_bw_inv an awkward name; would something like
bw_ratio or so be more accurate?

> +	if (global_rt_runtime() == RUNTIME_INF)
> +		dl_rq->deadline_bw_inv = 1 << 8;
> +	else
> +		dl_rq->deadline_bw_inv =
> +			to_ratio(global_rt_runtime(), global_rt_period()) >> 12;

That's almost the same code; do we want a helper function?

>  
>  u64 grub_reclaim(u64 delta, struct rq *rq)
>  {
> +	return (delta * rq->dl.running_bw * rq->dl.deadline_bw_inv) >> 20 >> 8;
>  }

At which point we might want a note about how this doesn't overflow I
suppose.

Also:

	delta *= rq->dl.running_bw;
	delta *= rq->dl.bw_ratio;
	delta >>= 20 + 8;

	return delta;

Might be more readable ?

Alternatively:

	delta = (delta * rq->dl.running_bw) >> 8;
	delta = (delta * rq->dl.bw_ratio) >> 20;

	return delta;

But I doubt we care about those extra 8 bit of space; delta should not
be over 36 bits (~64 seconds) anyway I suppose.

Thread

[RFC v5 5/9] sched/deadline: do not reclaim the whole CPU bandwidth luca abeni <luca.abeni@santannapisa.it> - 2017-03-23 21:00 +0100
  Re: [RFC v5 5/9] sched/deadline: do not reclaim the whole CPU  bandwidth Peter Zijlstra <peterz@infradead.org> - 2017-03-24 15:10 +0100
    Re: [RFC v5 5/9] sched/deadline: do not reclaim the whole CPU  bandwidth luca abeni <luca.abeni@santannapisa.it> - 2017-03-24 23:00 +0100
      Re: [RFC v5 5/9] sched/deadline: do not reclaim the whole CPU  bandwidth Steven Rostedt <rostedt@goodmis.org> - 2017-03-25 03:40 +0100
        Re: [RFC v5 5/9] sched/deadline: do not reclaim the whole CPU  bandwidth Peter Zijlstra <peterz@infradead.org> - 2017-03-27 10:40 +0200

csiph-web