Messages in this thread | | | Date | Wed, 7 Oct 2020 12:11:57 -0400 (EDT) | From | Mathieu Desnoyers <> | Subject | Re: [RFC PATCH 2/3] sched: membarrier: cover kthread_use_mm (v3) |
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----- On Oct 7, 2020, at 12:08 PM, Peter Zijlstra peterz@infradead.org wrote:
> On Wed, Oct 07, 2020 at 11:39:30AM -0400, Mathieu Desnoyers wrote: >> Moving the membarrier_switch_mm to cover kthread cases was to ensure (2), but if >> we >> add a p->mm NULL check in the global expedited iteration, I think we would be OK >> leaving the stale runqueue's membarrier state while in lazy tlb state. >> >> As far as (1) is concerned, I think your idea would work, because as you say we >> will >> have the proper barriers in kthread use/unuse mm. >> >> I just wonder whether having this stale membarrier state for lazy tlb is >> warranted >> performance-wise, as it adds complexity: the rq membarrier state will therefore >> not be >> relevant when we are in lazy tlb mode. >> >> Thoughts ? > > Well, the way I got here was that I considered the membarrier state > update tied to switch_mm(), and in that regard my proposal is a > simplification.
Sounds good.
So for the loop check, do we need it to be:
if ((p->flags & PF_KTHREAD) && !p->mm) continue;
Or can it simply become:
if (!p->mm) continue;
Because AFAIU only PF_KTHREAD can have NULL p->mm (?)
Thanks,
Mathieu
-- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com
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