Re: [PATCH] less tlb flush in unmap_vmas

Nick Piggin
2006-03-22T04:53:49Z

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.

One option I've been looking into is my "mmu gather in-place" that
never needs extra tlb flushes and is always preemptible... so that
may be a way forward.

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