On Sat, Mar 04, 2006 at 01:41:44PM -0800, David S. Miller ([email protected]) wrote:
> From: Jan Engelhardt <[email protected]>
> Date: Sat, 4 Mar 2006 19:46:22 +0100 (MET)
>
> > Does this buy the normal standard desktop user anything?
>
> Absolutely, it optimizes end-node performance.
It really depends on how it is used.
According to investigation made for kevent based FS AIO reading,
get_user_pages() performange graph looks like sqrt() function
with plato starting on about 64-80 pages on Xeon 2.4Ghz with 1Gb of ram,
while memcopy() is linear, so it can be noticebly slower than
copy_to_user() if get_user_pages() is used aggressively, so userspace
application must reuse the same, already grabbed buffer for maximum
performance, but Intel folks did not provide theirs usage case and any
benchmarks as far as I know.
--
Evgeniy Polyakov
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