Re: efficient copy_to_user and copy_from_user routines in Linux

[Hirokazu Takahashi]

Hello,

I have a patch which let sendmsg use copy_from_user instead of
csum_and_copy_from_user when a NIC supports HW-checksumming.
It just works on kernel 2.4, I haven't ported it on kernel 2.5 yet.
If you want it I'll port it after I come back from OTTAWA.

You can get the patch against kernel 2.4 from
ftp://ftp.valinux.co.jp/pub/people/taka/tune/2.4.17/va-udptcpchecksum-2.4.17-test1.patch

Would you try it?

> > I changed tcp to use a different copy if either source or dest were
> > not eight-byte aligned, and found that the resulting improvement
> > across a mixed networking load was only 1%.  Your numbers are higher,
> > so perhaps there are different alignments in the mix...
> 
> Did you look at sender or changed both of the functions?
> 
> After that accident TCP was changed and it does not use copy_from_user more,
> it does copy_and_csum even when no checksum is required. So, his results
> on sender side (except for strange anomaly at msg size 8K) just confirm
> nil effect of copy_from_user.
> 
> What's about copy_to_user, we forgot about this at all,
> worrying mostly about sender side. :-)

Thank you,
Hirokazu Takahashi.