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Message-ID: <20141021233933.GB2577@intel.com>
Date: Wed, 22 Oct 2014 07:39:33 +0800
From: Yuyang Du <yuyang.du@...el.com>
To: Peter Zijlstra <peterz@...radead.org>
Cc: mingo@...hat.com, linux-kernel@...r.kernel.org, pjt@...gle.com,
bsegall@...gle.com, arjan.van.de.ven@...el.com,
len.brown@...el.com, rafael.j.wysocki@...el.com,
alan.cox@...el.com, mark.gross@...el.com, fengguang.wu@...el.com
Subject: Re: [RESEND PATCH 2/3 v5] sched: Rewrite per entity runnable load
average tracking
On Tue, Oct 21, 2014 at 04:54:35PM +0200, Peter Zijlstra wrote:
>
> In the thread here: lkml.kernel.org/r/1409094682.29189.23.camel@...irtualBox
> there are concerns about the error bounds of such constructs. We can
> basically 'leak' nr_cpus * threshold, which is potentially a very large
> number.
>
> Do we want to introduce the force updated to combat this?
So introduce a force update here like:
+static inline void update_tg_load_avg(struct cfs_rq *cfs_rq, int force)
...
+ if (force || abs(delta) > cfs_rq->tg_load_avg_contrib / 64) {
That is good. In general, I have been lacking a theory about what threshold
should be concerning overhead vs. accuracy. But I think adding a force here
provides us an option to better comply with the theory if we have it.
Thanks,
Yuyang
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