linux-kernel - Re: weird loadavg on idle machine post 5.7

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Message-ID: <20200703205153.GA19901@codemonkey.org.uk>
Date:   Fri, 3 Jul 2020 16:51:53 -0400
From:   Dave Jones <davej@...emonkey.org.uk>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Mel Gorman <mgorman@...hsingularity.net>,
        Linux Kernel <linux-kernel@...r.kernel.org>, mingo@...nel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: weird loadavg on idle machine post 5.7

On Fri, Jul 03, 2020 at 12:40:33PM +0200, Peter Zijlstra wrote:
 
 > So ARM/Power/etc.. can speculate the load such that the
 > task_contributes_to_load() value is from before ->on_rq.
 > 
 > The compiler might similar re-order things -- although I've not found it
 > doing so with the few builds I looked at.
 > 
 > So I think at the very least we should do something like this. But i've
 > no idea how to reproduce this problem.
 > 
 > Mel's patch placed it too far down, as the WF_ON_CPU path also relies on
 > this, and by not resetting p->sched_contributes_to_load it would skew
 > accounting even worse.

looked promising the first few hours, but as soon as it hit four hours
of uptime, loadavg spiked and is now pinned to at least 1.00

	Dave