Re: performance: memcpy vs. __copy_tofrom_user

Paul Mackerras wrote:

Dominik Bozek writes:

  

quoted

Actually I made couple of other tests on that mpc8313. Most of them are
to ugly to publish them, but... My problem is that I have to boost the
gigabit interface on the mpc8313. I made simple substitution and
__copy_tofrom_user was used instead of memcpy. I know, it's wrong, but I
speedup that way the network interface for about 10%.
    

Very interesting.  Can you work out where memcpy is being called on
the network data?  I wouldn't have expected that.
  

I'm not the fastest, but I will. Just need some time.

There is actually no strong reason not to use __copy_tofrom_user as
memcpy, in fact, as long as we are sure that source and destination
are both cacheable.
  

My board doesn't have graphics, sound,...  so I don't know if and how it
touch that subsystems, but for sure ext2 fail. Interesting because it
was a ramdisk. Remember, that it was very tricky test, don't make any
wrong conclusion out of it.

Dominik