linux-kernel - Re: [PATCH] sched/schedutil : optimize utilization scaling for guest kernel

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Message-ID: <20180829124503.GU24124@hirez.programming.kicks-ass.net>
Date:   Wed, 29 Aug 2018 14:45:03 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Vincent Guittot <vincent.guittot@...aro.org>
Cc:     mingo@...nel.org, linux-kernel@...r.kernel.org, kernellwp@...il.com
Subject: Re: [PATCH] sched/schedutil : optimize utilization scaling for guest
 kernel

On Wed, Aug 29, 2018 at 10:51:42AM +0200, Vincent Guittot wrote:
> Scaling the utilization of CPUs with irq util_avg in schedutil doesn't give
> any benefit and just waste CPU cycles when irq time is not accounted but
> only steal time.
> Add an internal _scale_irq_capacity() for scale_rt_capacity but scale
> cpu utilization in schedutil only if we are accounting irq time.

This makes a mess of things; also it doesn't really do what it says.

Even if we have CONFIG_IRQ_TIME_ACCOUNTING, that doesn't mean we do it,
just that it is capable.