Messages in this thread | | | Date | Wed, 16 Sep 2020 23:39:28 +0800 | From | Peng Liu <> | Subject | Re: [PATCH] sched/deadline: Fix sched_dl_global_validate() |
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On Wed, Sep 16, 2020 at 11:42:03AM +0200, Juri Lelli wrote: > Hi, > > On 15/09/20 23:20, Peng Liu wrote: > > When user changes sched_rt_{runtime, period}_us, then > > > > sched_rt_handler() > > --> sched_dl_bandwidth_validate() > > { > > new_bw = global_rt_runtime()/global_rt_period(); > > > > for_each_possible_cpu(cpu) { > > dl_b = dl_bw_of(cpu); > > if (new_bw < dl_b->total_bw) > > ret = -EBUSY; > > } > > } > > > > Under CONFIG_SMP, dl_bw is per root domain , but not per CPU, > > dl_b->total_bw is the allocated bandwidth of the whole root domain. > > we should compare dl_b->total_bw against cpus*new_bw, where 'cpus' > > is the number of CPUs of the root domain. > > Hummm, I think you are right. Guess nobody played a lot with changing > global values. :-/ > > > Also, below annotation(in kernel/sched/sched.h) implied implementation > > only appeared in SCHED_DEADLINE v2[1], then deadline scheduler kept > > evolving till got merged(v9), but the annotation remains unchanged, > > meaningless and misleading, correct it. > > > > * With respect to SMP, the bandwidth is given on a per-CPU basis, > > * meaning that: > > * - dl_bw (< 100%) is the bandwidth of the system (group) on each CPU; > > * - dl_total_bw array contains, in the i-eth element, the currently > > * allocated bandwidth on the i-eth CPU. > > > > [1] https://lkml.org/lkml/2010/2/28/119 > > > > Signed-off-by: Peng Liu <iwtbavbm@gmail.com> > > --- > > In fact, I'm not 100% sure that's a bug, since it's too 'obvious' and > > not newly introduced code. > > > > Also, the introduced #ifdef...#endif pairs look ugly, I have no idea > > how to eliminate them. Ideas and comments are welcome. Thanks. > > Can't we just use dl_bw_cpus() ? >
Oh, good idea, I will have a try. Thanks for your time!
> Thanks, > Juri >
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