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Date: Thu, 19 May 2016 06:51:15 +0800
From: Yuyang Du <yuyang.du@intel.com>
To: Matt Fleming <matt@codeblueprint.co.uk>
Cc: Peter Zijlstra <peterz@infradead.org>, Ingo Molnar <mingo@kernel.org>,
        linux-kernel@vger.kernel.org, Byungchul Park <byungchul.park@lge.com>,
        Frederic Weisbecker <fweisbec@gmail.com>,
        Luca Abeni <luca.abeni@unitn.it>,
        "Rafael J . Wysocki" <rafael.j.wysocki@intel.com>,
        Rik van Riel <riel@redhat.com>, Thomas Gleixner <tglx@linutronix.de>,
        Wanpeng Li <wanpeng.li@hotmail.com>,
        Mel Gorman <mgorman@techsingularity.net>,
        Mike Galbraith <umgwanakikbuti@gmail.com>
Subject: Re: [RFC][PATCH 5/5] sched/core: Add debug code to catch missing
 update_rq_clock()
Message-ID: <20160518225115.GA17721@intel.com>
References: <1463082593-27777-1-git-send-email-matt@codeblueprint.co.uk>
 <1463082593-27777-6-git-send-email-matt@codeblueprint.co.uk>
 <20160515021439.GC8790@intel.com>
 <20160516094638.GB6574@codeblueprint.co.uk>
 <20160516201109.GD8790@intel.com>
 <20160517122415.GD21993@codeblueprint.co.uk>
 <20160517190127.GE8790@intel.com>
 <20160518084120.GF21993@codeblueprint.co.uk>
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On Wed, May 18, 2016 at 09:41:20AM +0100, Matt Fleming wrote:
> On Wed, 18 May, at 03:01:27AM, Yuyang Du wrote:
> > 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.
> 
> That was sloppy on my part but intentional because that's what the
> code looks like in tip/sched/core today.
 
Sure, rq->clock_update_flags = 0 is itself all right, just say what you do.

> It was purely meant to demonstrate that setting RQCF_UPDATE just
> because RQCF_ACT_SKIP is set does not make sense. You can replace the
> clearing line with the correct bit masking operation.
 
I don't understand how you demonstrated that does not make sense. Anways,
you sort it out.

> But I get it, the pseudo-code was confusing. I'll send out a v2.
>
> > 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...
> 
> Right, I wouldn't actually clear RQCF_UPDATE in v2 of this patch.
> 
> > In addition, it looks like multiple skips are possible, so:
>  
> I'm not sure what you mean, could you elaborate?
> 
> > update_rq_clock() {
> >         rq->clock_update_flags |= RQCF_UPDATE;
> > 
> >         ...
> > }
> > 
> > instead of clearing the skip flag there.
> 
> Huh? RQCF_*_SKIP are not cleared in update_rq_clock().

Yeah, I previously cleared the SKIP bit, which is not right, so I corrected.