Messages in this thread | | | From | Wander Lairson Costa <> | Date | Mon, 30 Jan 2023 11:58:52 -0300 | Subject | Re: [PATCH v2 1/4] sched/task: Add the put_task_struct_atomic_safe function |
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On Mon, Jan 30, 2023 at 11:47 AM Valentin Schneider <vschneid@redhat.com> wrote: > > On 30/01/23 08:49, Wander Lairson Costa wrote: > > On Fri, Jan 27, 2023 at 12:55 PM Valentin Schneider <vschneid@redhat.com> wrote: > >> > >> On 23/01/23 14:24, Wander Lairson Costa wrote: > >> > Therefore (if I am correct in my assumption), it would make sense for > >> > only some call sites to pay the overhead price for it. But this is > >> > just a guess, and I have no evidence to support my claim. > >> > >> My worry here is that it's easy to miss problematic callgraphs, and it's > >> potentially easy for new ones to creep in. Having a solution within > >> put_task_struct() itself would prevent that. > >> > > > > We could add a WARN_ON statement in put_task_struct() to detect such cases. > > > > Anyone running their kernel with DEBUG_ATOMIC_SLEEP should be able to > detect misuse, but it doesn't change that some callgraphs will only > materialize under certain hardware/configuration combos. >
If we put a WARN_ON in put_task_struct(), we catch cases where the reference count didn't reach zero.
> >> Another thing, if you look at release_task_stack(), it either caches the > >> outgoing stack for later use, or frees it via RCU (regardless of > >> PREEMPT_RT). Perhaps we could follow that and just always punt the freeing > >> of the task struct to RCU? > >> > > > > That's a point. Do you mean doing that even for !PREEMPT_RT? > > Could be worth a try?
Sure. But I would do it only for PREEMPT_RT.
> I think because of the cache thing the task stack is > a bit less aggressive wrt RCU callback processing, but at a quick glance I > don't see any fundamental reason why the task_struct itself can't be given > the same treatment. >
Any idea about tests to catch performance regressions?
I
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