RE: [PATCH] less tlb flush in unmap_vmas

From: Chen, Kenneth W
Date: Wed Mar 22 2006 - 02:41:27 EST

Nick Piggin wrote on Tuesday, March 21, 2006 11:30 PM
> > Chen, Kenneth W wrote:
> > Interesting. In the old day, since mm->page_table_lock is held for the
> > entire unmap_vmas function, it was beneficial to introduce periodic
> > reschedule point and to drop the spin lock under pressure. Now that the
> > page table lock is fine-grained and is pushed into zap_pte_range(), I
> > would think scheduling latency would improve from lock contention
> > avoidance point of view. It is not the case?
> >
> Well mmu_gather uses a per-cpu data structure and is non preemptible,
> which I guess is one of the main reasons why we have this preemption
> here.
> You're right that another good reason would be ptl lock contention,
> however I don't think that alleviating that problem alone would allow
> longer mmu_gather scheduling latencies, because the longest latency
> is still the mmu_gather <--> mmu_finish span.

OK, I think it would be beneficial to take a latency measurement again,
just to see how it perform now a day. The dynamics might changed.

- Ken

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