Re: MMU & cache trick: page flips on COW?
Mark Hemment (markhe@sco.COM)
Tue, 14 Jan 1997 10:55:27 +0000 (GMT)
David S. Miller wrote:
> If you truly want get around the no-write-allocate problem, do
> something to the memcpy code itself which helps the situation. I
> believe the memcpy etc. code in GNU libc written by Torbjourn
> Granlund
> does in fact do a quick read of the first word in each cache line
> being copied to in order to work around this problem specifically,
> and the speed increase does show up.
Yep, does offer a 'local' speed improve, at the expensive of filling
half my L1 data cache! One page I don't need, and one page I _might_
need. But if someone wants to benchmark real-life suitations and
prove my sceptism wrong...
csum_partial_copy() can use the same technique for increasing
performance, but the hidden overhead probably outweights the
benefits.
Regards,
markhe