linux-kernel - Re: [RFC][PATCH 5/5] sched/core: Add debug code to catch missing update_rq

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Date:	Wed, 18 May 2016 03:01:27 +0800
From:	Yuyang Du <yuyang.du@...el.com>
To:	Matt Fleming <matt@...eblueprint.co.uk>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org,
	Byungchul Park <byungchul.park@....com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Luca Abeni <luca.abeni@...tn.it>,
	"Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
	Rik van Riel <riel@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Wanpeng Li <wanpeng.li@...mail.com>,
	Mel Gorman <mgorman@...hsingularity.net>,
	Mike Galbraith <umgwanakikbuti@...il.com>
Subject: Re: [RFC][PATCH 5/5] sched/core: Add debug code to catch missing
 update_rq_clock()

On Tue, May 17, 2016 at 01:24:15PM +0100, Matt Fleming wrote:
> So, if the code looks like the following, either now or in the future,
> 
> static void __schedule(bool preempt)
> {
> 	...
> 	/* Clear RQCF_ACT_SKIP */
> 	rq->clock_update_flags = 0;
> 	...
> 	delta = rq_clock();
> }
 
Sigh, you even said "Clear RQCF_ACT_SKIP", but you not only clear it,
you clear everything. And if you clear the RQCF_UPDATE also (maybe you
shouldn't, but actually it does not matter), of course you will get
a warning...

In addition, it looks like multiple skips are possible, so:

update_rq_clock() {
        rq->clock_update_flags |= RQCF_UPDATE;

        ...
}

instead of clearing the skip flag there.