Ben,
    I got to bring up Linux on one of the 440 processors with out L1
dcache to do some bench marking  and compare with  L1 d-cache enabled. =20

I am avoiding any references to dcbz ,dcbt and dcbst .   Also the TLB's
are created with cache inhibited. I looked at lwarx/stwcx description,
there seem to be no dependency on L1 cache.

I don't see any critical exceptions or traps. All I  see is /init/bin
failing to execute because data is corrupted.=20

Thanks,
Marri


-----Original Message-----
From: Benjamin Herrenschmidt [mailto:benh@kernel.crashing.org]=20
Sent: Tuesday, September 30, 2008 2:31 PM
To: Tirumala Reddy Marri
Cc: Olof Johansson; linuxppc-dev@ozlabs.org
Subject: RE: Disabling L1 D-cache and side effects

On Tue, 2008-09-30 at 09:57 -0700, Tirumala Reddy Marri wrote:

Ben,
  Thanks for the response. I am wondering how user space would get=20
affected by absence of L1 Dcache.

You didn't answer my question :-)

Well, as I said, things like lwarx/stwcx not working, dcbz taking
alignment exceptions, etc...

Ben.

Thanks,
Marri
=20
-----Original Message-----
From: Benjamin Herrenschmidt [mailto:benh@kernel.crashing.org]
Sent: Tuesday, September 30, 2008 12:16 AM
To: Tirumala Reddy Marri
Cc: Olof Johansson; linuxppc-dev@ozlabs.org
Subject: RE: Disabling L1 D-cache and side effects
=20
On Mon, 2008-09-29 at 14:38 -0700, Tirumala Reddy Marri wrote:

quoted

Could you please point me to the which does the Critical error=20
(Machine
Check) recovery. BTW I am successful booting the Linux until rootfs=20
is

=20

quoted

being mounted. It fails to mount the Linux saying that blocks are=20
corrupted in file system. I had to modify lots of initial bring up=20
code to disable D-cache and make sure all TLB's are cache inhibited.
Ando also made sure none of the misc_32.S , entry_32.S and head.S=20
makes any references to d-cache.

=20
Why the heck are you doing that btw ? AFAIK, as Olof says, things like

atomic operations will not work, dcbz neither etc... it's likely that=20
even if you manage to plaster around all of this in the kernel,=20
whatever userspace code you'll try to run in userspace will blow up

too...

=20
Cheers,
Ben.