linux-kernel - Re: [RFC 8/8] Do not reclaim the whole CPU bandwidth

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Message-ID: <20160203113019.GT3947@e106622-lin>
Date:	Wed, 3 Feb 2016 11:30:19 +0000
From:	Juri Lelli <juri.lelli@....com>
To:	Luca Abeni <luca.abeni@...tn.it>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>
Subject: Re: [RFC 8/8] Do not reclaim the whole CPU bandwidth

Hi Luca, Peter,

On 02/02/16 21:53, Luca Abeni wrote:
> On Wed, 27 Jan 2016 15:44:22 +0100
> Peter Zijlstra <peterz@...radead.org> wrote:
> 
> > On Tue, Jan 26, 2016 at 01:52:19PM +0100, luca abeni wrote:
> > 
> > > > The trouble is with interfaces. Once we expose them we're stuck
> > > > with them. And from that POV I think an explicit SCHED_OTHER
> > > > server (or a minimum budget for a slack time scheme) makes more
> > > > sense.
> > 
> > > I am trying to work on this.
> > > Which kind of interface is better for this? Would adding something
> > > like /proc/sys/kernel/sched_other_period_us
> > > /proc/sys/kernel/sched_other_runtime_us
> > > be ok?
> > > 
> > > If this is ok, I'll add these two procfs files, and store
> > > (sched_other_runtime / sched_other_period) << 20 in the runqueue
> > > field which represents the unreclaimable utilization (implementing
> > > hierarchical SCHED_DEADLINE/CFS scheduling right now is too complex
> > > for this patchset... But if the exported interface is ok, it can be
> > > implemented later).
> > > 
> > > Is this approach acceptable? Or am I misunderstanding your comment?
> > 
> > No, I think that's fine.
> So, I implemented this idea (/proc/sys/kernel/sched_other_period_us
> and /proc/sys/kernel/sched_other_runtime_us to set the unreclaimable
> utilization), and some initial testing seems to show that it works fine.
> 

Sorry for not saying this before, but why can't we use the existing
sched_rt_runtime_us/sched_rt_runtime_period cap for this? I mean, other
will have (1 - rt_runtime_ratio) available to run.

Best,

- Juri