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

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Message-ID: <20160127144422.GS6357@twins.programming.kicks-ass.net>
Date:	Wed, 27 Jan 2016 15:44:22 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	luca abeni <luca.abeni@...tn.it>
Cc:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
	Juri Lelli <juri.lelli@....com>
Subject: Re: [RFC 8/8] Do not reclaim the whole CPU bandwidth

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.

Altough now you have me worrying about per root_domain settings and the
like. But I think we can do that with additional interfaces, if needed.

So yes, please go with that.

And agreed, a full CFS server is a bit outside scope for this patch-set.