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

From	Matt Fleming <matt@codeblueprint.co.uk>
Newsgroups	linux.kernel
Subject	Re: [RFC][PATCH 5/5] sched/core: Add debug code to catch missing update_rq_clock()
Date	2016-05-18 10:50 +0200
Message-ID	<rA5l1-87e-37@gated-at.bofh.it> (permalink)
References	(2 earlier) <rzg8Z-u7-317@gated-at.bofh.it> <rznjX-5fy-3@gated-at.bofh.it> <rzEkN-7L0-1@gated-at.bofh.it> <rzMim-4v6-19@gated-at.bofh.it> <rzZIC-4vM-11@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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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.

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.

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().

Thread

[RFC][PATCH 5/5] sched/core: Add debug code to catch missing update_rq_clock() Matt Fleming <matt@codeblueprint.co.uk> - 2016-05-12 22:00 +0200
  Re: [RFC][PATCH 5/5] sched/core: Add debug code to catch missing  update_rq_clock() Yuyang Du <yuyang.du@intel.com> - 2016-05-16 04:10 +0200
    Re: [RFC][PATCH 5/5] sched/core: Add debug code to catch missing  update_rq_clock() Matt Fleming <matt@codeblueprint.co.uk> - 2016-05-16 11:50 +0200
      Re: [RFC][PATCH 5/5] sched/core: Add debug code to catch missing  update_rq_clock() Yuyang Du <yuyang.du@intel.com> - 2016-05-17 06:00 +0200
        Re: [RFC][PATCH 5/5] sched/core: Add debug code to catch missing  update_rq_clock() Matt Fleming <matt@codeblueprint.co.uk> - 2016-05-17 14:30 +0200
          Re: [RFC][PATCH 5/5] sched/core: Add debug code to catch missing  update_rq_clock() Yuyang Du <yuyang.du@intel.com> - 2016-05-18 04:50 +0200
            Re: [RFC][PATCH 5/5] sched/core: Add debug code to catch missing  update_rq_clock() Matt Fleming <matt@codeblueprint.co.uk> - 2016-05-18 10:50 +0200
              Re: [RFC][PATCH 5/5] sched/core: Add debug code to catch missing  update_rq_clock() Yuyang Du <yuyang.du@intel.com> - 2016-05-19 08:40 +0200

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