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

Yuyang Du
2016-05-19T06:32:34Z

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.