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Re: [RFC v3 1/6] Track the active utilisation

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  Re: [RFC v3 1/6] Track the active utilisation Peter Zijlstra <peterz@infradead.org> - 2016-11-18 15:30 +0100
    Re: [RFC v3 1/6] Track the active utilisation luca abeni <luca.abeni@unitn.it> - 2016-11-18 16:20 +0100
      Re: [RFC v3 1/6] Track the active utilisation Peter Zijlstra <peterz@infradead.org> - 2016-11-18 16:30 +0100
    Re: [RFC v3 1/6] Track the active utilisation Steven Rostedt <rostedt@goodmis.org> - 2016-11-18 17:50 +0100

#1525393 — Re: [RFC v3 1/6] Track the active utilisation

On Tue, Oct 25, 2016 at 09:58:11AM -0400, Steven Rostedt wrote:

> I agree with Daniel, especially since I don't usually trust the
> compiler. And the added variable is more of a distraction as it doesn't
> seem to have any real purpose.

I don't think there's anything here to trust the compiler on. Either
it inlines or it doesn't, it should generate 'correct' code either way.

If it doesn't inline, its a dumb compiler and it will make these dumb
decisions throughout the tree and your kernel will be slow, not my
problem really ;-)

That said, I agree that the single line thing is actually easier to
read.

That said; there's something to be said for:

	u64 running_bw;

static void add_running_bw(struct sched_dl_entity *dl_se, struct dl_rq *dl_rq)
{
	u64 old = dl_rq->running_bw;

	dl_rq->running_bw += dl_se->dl_bw;
	SCHED_WARN_ON(dl_rq->running_bw < old); /* overflow */
}

static void sub_running_bw(struct sched_dl_entity *dl_se, struct dl_rq *dl_rq)
{
	u64 old = dl_rq->running_bw;

	dl_rq->running_bw -= dl_se->dl_bw;
	SCHED_WARN_ON(dl_rq->running_bw > old); /* underflow */
}

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#1525456

On Fri, 18 Nov 2016 15:23:59 +0100
Peter Zijlstra <peterz@infradead.org> wrote:

> On Tue, Oct 25, 2016 at 09:58:11AM -0400, Steven Rostedt wrote:
> 
> > I agree with Daniel, especially since I don't usually trust the
> > compiler. And the added variable is more of a distraction as it
> > doesn't seem to have any real purpose.  
> 
> I don't think there's anything here to trust the compiler on. Either
> it inlines or it doesn't, it should generate 'correct' code either
> way.
> 
> If it doesn't inline, its a dumb compiler and it will make these dumb
> decisions throughout the tree and your kernel will be slow, not my
> problem really ;-)
> 
> That said, I agree that the single line thing is actually easier to
> read.

Ok; I already made that change locally.


> 
> That said; there's something to be said for:
> 
> 	u64 running_bw;

Ok; I originally made it signed because I wanted the "running_bw < 0"
check, but I can change it to "dl_rq->running_bw > old" (I did not
think about it).

I'll make these changes locally ASAP.


			Thanks,
				Luca

> 
> static void add_running_bw(struct sched_dl_entity *dl_se, struct
> dl_rq *dl_rq) {
> 	u64 old = dl_rq->running_bw;
> 
> 	dl_rq->running_bw += dl_se->dl_bw;
> 	SCHED_WARN_ON(dl_rq->running_bw < old); /* overflow */
> }
> 
> static void sub_running_bw(struct sched_dl_entity *dl_se, struct
> dl_rq *dl_rq) {
> 	u64 old = dl_rq->running_bw;
> 
> 	dl_rq->running_bw -= dl_se->dl_bw;
> 	SCHED_WARN_ON(dl_rq->running_bw > old); /* underflow */
> }
> 
> 

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#1525462

On Fri, Nov 18, 2016 at 04:10:17PM +0100, luca abeni wrote:

> Ok; I originally made it signed because I wanted the "running_bw < 0"
> check, but I can change it to "dl_rq->running_bw > old" (I did not
> think about it).

Happy accident of me staring at unsigned over/under-flow for the past
several days :-)

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#1525511

On Fri, 18 Nov 2016 15:23:59 +0100
Peter Zijlstra <peterz@infradead.org> wrote:

 
> That said; there's something to be said for:
> 
> 	u64 running_bw;
> 
> static void add_running_bw(struct sched_dl_entity *dl_se, struct dl_rq *dl_rq)
> {
> 	u64 old = dl_rq->running_bw;
> 
> 	dl_rq->running_bw += dl_se->dl_bw;
> 	SCHED_WARN_ON(dl_rq->running_bw < old); /* overflow */
> }
> 
> static void sub_running_bw(struct sched_dl_entity *dl_se, struct dl_rq *dl_rq)
> {
> 	u64 old = dl_rq->running_bw;
> 
> 	dl_rq->running_bw -= dl_se->dl_bw;
> 	SCHED_WARN_ON(dl_rq->running_bw > old); /* underflow */
> }
> 

Acked-by: me

-- Steve

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