Messages in this thread | | | Subject | Re: [PATCH v3 03/14] sched/core: uclamp: add CPU's clamp groups accounting | From | Dietmar Eggemann <> | Date | Wed, 15 Aug 2018 11:37:13 +0200 |
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On 08/14/2018 06:49 PM, Patrick Bellasi wrote: > Hi Dietmar! > > On 14-Aug 17:44, Dietmar Eggemann wrote: >> On 08/06/2018 06:39 PM, Patrick Bellasi wrote:
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>> This one indicates that there are some holes in your ref-counting. > > Not really, this has been added not because I've detected a refcount > issue... but because it was suggested as a possible safety check in a > previous code review comment: > > https://lore.kernel.org/lkml/20180720151156.GA31421@e110439-lin/ > >> It's probably easier to debug that there is still a task but the >> uc_grp[group_id].tasks value == 0 (A). I assume the other problem exists as >> well, i.e. last task and uc_grp[group_id].tasks > 1 (B)? >> >> You have uclamp_cpu_[get/put](_id)() in [enqueue/dequeue]_task. >> >> Patch 04/14 introduces its use in uclamp_task_update_active(). >> >> Do you know why (A) (and (B)) are happening? > > I've never saw that warning in my tests so far so, again, the warning > is there just to support testing/debugging when refcounting code > is/will be touched in the future. That's also the reason why is > SCHED_DEBUG protected.
Ah, OK, I thought you really see it more often and that it also relate to Pavan's comment on 02/14 about the missing treatment of exiting tasks.
If this is only for testing/debugging, I would suggest a simple one line BUG_ON()
You find CONFIG_SCHED_DEBUG=y in production kernels as well.
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> Here you right, I would say that it should always be: > > clamp_value <= uc_cpu->value[clamp_id] > > since this matches the update done at the end of uclamp_cpu_get_id(): > > if (uc_cpu->value[clamp_id] < clamp_value) > uc_cpu->value[clamp_id] = clamp_value; > > Perhaps we can add another safety check here, similar to the one > above, to have something like: > > clamp_value = uc_grp[group_id].value; > #ifdef SCHED_DEBUG > if (unlikely(clamp_value > uc_cpu->value[clamp_id])) { > WARN(1, "invalid CPU[%d] clamp group [%d:%d] value\n", > cpu_of(rq), clamp_id, group_id); > #endif > if (clamp_value == uc_cpu->value[clamp_id]) > uclamp_cpu_update(rq, clamp_id);
Yes, but I would prefer a BUG_ON() one liner.
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