Re: 2.5.50-BK + 24 CPUs

From: Manfred Spraul (
Date: Mon Dec 09 2002 - 16:12:58 EST

David S. Miller wrote:

> From: Manfred Spraul <>
> Date: Mon, 09 Dec 2002 18:03:10 +0100
> Unfortunately zero-copy doesn't help to avoid the schedules:
> Zero copy just avoid the copy to kernel - you still need one schedule
> for each page to be transfered.
>The zerocopy patches copied up to 64k (or rather, 16 pages, something
>like that) at once, that's going to lead to 16 times less schedules.
>The 64k number was decided arbitrarily (it's what freebsd's pipe code
>uses) and it can be experimented with.
Only if user space writes in 64 kB chunks - if user space writes 4 kB
chunks, then zerocopy doesn't help much against schedule [depending on
the implementation, it halves the number of schedules].
And page table tricks (COW) tricks are not acceptable.


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