Messages in this thread | | | From | "Chen, Kenneth W" <> | Subject | RE: [PATCH] less tlb flush in unmap_vmas | Date | Tue, 21 Mar 2006 23:15:13 -0800 |
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Nick Piggin wrote on Tuesday, March 21, 2006 8:53 PM > Shaohua Li wrote: > >In unmaping region, if current task doesn't need reschedule, don't do a > >tlb_finish_mmu. This can reduce some tlb flushes. > > > >In the lmbench tests, this patch gives 2.1% improvement on exec proc > >item and 4.2% on sh proc item. > > The problem with this is that by the time we _do_ determine that a > reschedule is needed, we might have built up a huge amount of work > to do (which can probably be as much if not more exensive per-page > as the unmapping), so scheduling latency can still be unacceptable > so I'm afraid I don't think we can include this patch.
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?
- Ken
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