[PATCH] powerpc: tiny memcpy_(to|from)io optimisation
Albrecht Dreß
albrecht.dress at arcor.de
Fri May 29 05:50:24 EST 2009
Am 28.05.09 18:13 schrieb(en) Joakim Tjernlund:
> hmm, these do look a bit unoptimal anyway. Any reason not to write
> them something like below(written by me for uClibc long time ago).
> You will have to add eieio()/sync
No (and I wasn't aware of the PPC pre-inc vs. post-inc stuff) - I just
stumbled over this while fixing mtd accesses to the MPC5200's Local Bus
in 16-bit mode which doesn't allow byte accesses. And I didn't want to
go too deep into this as the real fix for me is actually somewhat
different...
> /* PPC can do pre increment and load/store, but not post increment
> and load/store.
> Therefore use *++ptr instead of *ptr++. */
[snip]
> copy_chunks:
> do {
> /* make gcc to load all data, then store it */
> tmp1 = *(unsigned long *)(tmp_from+4);
> tmp_from += 8;
> tmp2 = *(unsigned long *)tmp_from;
> *(unsigned long *)(tmp_to+4) = tmp1;
> tmp_to += 8;
> *(unsigned long *)tmp_to = tmp2;
> } while (--chunks);
Is this the same for all PPC cores, i.e. do they all benefit from
loading/storing 8 instead of 4 bytes?
Best, Albrecht.
-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: application/pgp-signature
Size: 189 bytes
Desc: not available
URL: <http://lists.ozlabs.org/pipermail/linuxppc-dev/attachments/20090528/b3e995a5/attachment.pgp>
More information about the Linuxppc-dev
mailing list