Re: [RFC][PATCH 5/5] sched/core: Add debug code to catch missing update_rq_clock()

[Yuyang Du]

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.