Re: [PATCH] 2/2 2.5.45 cleanup & add original copy_ro/from_user

Denis Vlasenko (vda@port.imtp.ilyichevsk.odessa.ua)
Sat, 2 Nov 2002 15:08:16 -0200

On 2 November 2002 10:09, Andi Kleen wrote:
> > That depends on size. If you do huge memcpy (say 1 mb) it still
> > wins by wide margin. Not that we do such huge operations often,
> > but code can check size and pick different routines for small
> > and big blocks
>
> The kernel nevers does such huge memcpys. It rarely does handle any
> buffer bigger than a page (4K)

Okay I take that.

How did you determined that movntXX stores are net loss?
I thought about that and didn't came to a working solution.

It's easy to time memcpy() but harder to measure susequent
cache misses when copied data gets accessed. We can read it
back after memcpy and measure memcpy()+read, but is entire
copy gets used immediately after memcpy() in real world usage?
We're in benchmarking hell :(

--
vda
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