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

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Message-ID: <20160114195904.GH6357@twins.programming.kicks-ass.net>
Date:	Thu, 14 Jan 2016 20:59:04 +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 Thu, Jan 14, 2016 at 04:24:53PM +0100, Luca Abeni wrote:
> Original GRUB tends to reclaim 100% of the CPU time... And this allows a
> "CPU hog" (i.e., a busy loop) to starve non-deadline tasks.
> To address this issue, allow the scheduler to reclaim only a specified
> fraction of CPU time.
> NOTE: the fraction of CPU time that cannot be reclaimed is currently
> hardcoded as (1 << 20) / 10 -> 90%, but it must be made configurable!

So the alternative is an explicit SCHED_OTHER server which is
configurable.

That would maybe fit in nicely with the DL based FIFO/RR servers from
this other pending project.

> --- a/kernel/sched/sched.h
> +++ b/kernel/sched/sched.h
> @@ -524,6 +524,10 @@ struct dl_rq {
>  	 * and decreased when a task blocks
>  	 */
>  	s64 running_bw;
> +	/* This is the amount of utilization that GRUB can not
> +         * reclaim (per runqueue)
> +         */
> +	s64 unusable_bw;


Wrong comment style and whitespace challenged.