Re: [PATCH] powerpc: POWER7 optimised memcpy using VMX and enhanced prefetch

[Jimi Xenidis <jimix@pobox.com>]

On Dec 17, 2012, at 5:33 AM, Anton Blanchard <anton@samba.org> wrote:

>=20
> Hi Jimi,
>=20
>> I know this is a little late, but shouldn't these power7 specific
>> thingies be in "obj-$(CONFIG_PPC_BOOK3S_64)". The reason I ask is
>> that my compiler pukes on "dcbtst" and as I deal with that I wanted
>> to point this out.
>=20
> I guess we could do that.

I think it is the right idea since it is unclear that your optimizations =
would actually help an embedded system where most of these cache =
prefetches are NOPs and only wait decode/dispatch cycles.

> It's a bit strange your assembler is
> complaining about the dcbtst instructions since we wrap them with
> power4:

Not really, the binutils is a little old (RHEL 6.2), unfortunately it =
_is_ the toolchain most people are using at the moment.
It will take me a while to get everyone using newer ones since most are =
scientists using the packages they get.

My suggestion was really for correctness,  My current patches for BG/Q =
introduce a macro replacement.
-jx


>=20
> .machine push
> .machine "power4"
>        dcbt    r0,r4,0b01000
>        dcbt    r0,r7,0b01010
>        dcbtst  r0,r9,0b01000
>        dcbtst  r0,r10,0b01010
>        eieio
>        dcbt    r0,r8,0b01010   /* GO */
> .machine pop
>=20
> Anton