> > > details, but I do know that using copy_from_user() is not a real
> > > improvement at least on x86 architecture.
> >
> > The same as bit is easy to explain. Its totally memory bandwidth limited
> > on current x86-32 processors. (Although I'd welcome demonstrations to
> > the contrary on newer toys)
>
> Nope. There are distinct alignment problems with movsl-based
> memcpy on PII and (at least) "Pentium III (Coppermine)", which is
> tested here:
...
> I have various scriptlets which generate the entire matrix.
>
> I think I ended up deciding that we should use movsl _only_
> when both src and dsc are 8-byte-aligned. And that when you
> multiply the gain from that by the frequency*size with which
> funny alignments are used by TCP the net gain was 2% or something.
Amazing! I beleived 4-byte-aligned was enough.
read/write systemcalls may also reduce their penalties.
> It needs redoing. These differences are really big, and this
> is the kernel's most expensive function.
>
> A little project for someone.
OK, if there is nobody who wants to do it I'll do it by myself.
> The tools are at http://www.zip.com.au/~/linux/cptimer.tar.gz
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/