Messages in this thread | | | Date | Mon, 6 Jul 2015 19:04:07 +0530 | From | Afzal Mohammed <> | Subject | Re: [PATCH] sched,fair: Remove > u32 weight handling for delta |
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Hi,
On Mon, Jul 06, 2015 at 01:44:30PM +0200, Peter Zijlstra wrote: > On Mon, Jul 06, 2015 at 08:14:37AM +0530, Afzal Mohammed wrote:
> > scaled down weight 'fact' would not be > u32 rather than unlikely as the > > values being passed for delta is either NICE_O_LOAD or the weight of the > > 'se' which would be a value that can be accomodated in a u32. > > This needs a bit more on why se->load.weight must fit u32 (its true, but > not evident from this text).
Okay, I will add an equivalent of the below to the log,
"se->load.weight can have either the values in prio_to_weight[] for cases where 'se' is a task or capped to MAX_SHARES (1 << 18) when it is a group. And these values can be accomodated in a u32.",
and send the patch, unless a negative opinion on the above.
> Now as long as we never call __calc_delta() on a rq weight -- which is a > sum of weights and can indeed be larger than u32, we can indeed remove > this.
My understanding is that we do not call __calc_delta() on rq weight.
> And I think we already assume such, see this story on why shift will > remain positive.
ok
> > The hunk being removed here > > would not make a difference to it as this is on scaled weight > u32. > > And pre-"9dbdb15553239" doesn't seem to have logical equivalent of hunk > > removed here either. > > -ENOPARSE.
Reading 9dbdb15553239 ("sched/fair: Rework sched_fair time accounting") again, realized that I am wrong on this, that was referring to the below statement removed in that commit,
if (likely(weight > (1UL << SCHED_LOAD_RESOLUTION))) tmp = (u64)delta_exec * scale_load_down(weight);
earlier came to a reasoning that as scale_load_down(weight) was not separately typecasted, value above u32 would be discarded, that non parsable statement meant that weight > u32 was not considered. Since cast has precedence over multiply, that statement of mine was wrong.
Regards Afzal
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