Messages in this thread | | | From | Vincent Guittot <> | Date | Fri, 30 Apr 2021 16:16:58 +0200 | Subject | Re: [PATCH v2] sched: Fix out-of-bound access in uclamp |
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On Fri, 30 Apr 2021 at 15:14, Quentin Perret <qperret@google.com> wrote: > > On Friday 30 Apr 2021 at 15:00:00 (+0200), Dietmar Eggemann wrote: > > On 30/04/2021 14:03, Vincent Guittot wrote: > > IMHO, this asks for > > > > min_t(unsigned int, clamp_value/UCLAMP_BUCKET_DELTA, UCLAMP_BUCKETS-1); > > Yep, that's what I have locally. > > > >> } > > >> > > >> static inline unsigned int uclamp_none(enum uclamp_id clamp_id) > > > > Looks like this will fix a lot of possible configs: > > > > nbr buckets 1-4, 7-8, 10-12, 14-17, *20*, 26, 29-32 ... > > > > We would still introduce larger last buckets, right? > > Indeed. The only better alternative I could see was to 'spread' the > error accross multiple buckets (e.g. make the last few buckets a bit > bigger instead of having all of it accumulated on the last one), but not > sure it is worth the overhead.
I don't think it's worth the overhead.
> > Suggestions are welcome though. > > > Examples: > > > > nbr_buckets delta last bucket size > > > > 20 51 +5 = 56 > > > > 26 39 +10 = 49 > > > > 29 35 +9 = 44 > > Yes the error can become worse in the relative sense with a large number > of buckets, but again the max is 20 so we should be fine? > > Thanks, > Quentin
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