No L2 Cache on PReP Machine

No L2 Cache on PReP Machine

[Hager, Johannes, HRD/AB]

Hi
I am usign Linux on the Motorola MVME3604 Board. This Board complies to the
PReP standard. So I configured the linux machine type to
"CHRP/PowerMac/PReP".
The kernel starts without showing any errors, but the problem is, that the
L2 cache of the board is not recognized by the kernel. Does the linux not
support L2 caches on PReP machines or is it another problem?

Best regards,
Johannes

** Sent via the linuxppc-embedded mail list. See http://lists.linuxppc.org/

Re: No L2 Cache on PReP Machine

[Adrian Cox]

On Thu, 2004-08-19 at 08:43, Hager, Johannes, HRD/AB wrote:

> I am usign Linux on the Motorola MVME3604 Board. This Board complies to the
> PReP standard. So I configured the linux machine type to
> "CHRP/PowerMac/PReP".
> The kernel starts without showing any errors, but the problem is, that the
> L2 cache of the board is not recognized by the kernel. Does the linux not
> support L2 caches on PReP machines or is it another problem?

Generally Linux expects the boot firmware to set up the L2 and L3 caches
on PowerPC machines. Are you quite sure (from benchmark timings) that
the L2 cache is not working? The MVME3604 has an L2 cache outside the
processor, and it should work transparently.

- Adrian Cox
Humboldt Solutions Ltd


** Sent via the linuxppc-embedded mail list. See http://lists.linuxppc.org/

RE: No L2 Cache on PReP Machine

[Hager, Johannes, HRD/AB]

Hi,

>Generally Linux expects the boot firmware to set up the L2 and L3 caches
>on PowerPC machines. Are you quite sure (from benchmark timings) that
>the L2 cache is not working? The MVME3604 has an L2 cache outside the
>processor, and it should work transparently.
First the /proc/cpuinfo file contains the following informations:
processor	: 0
cpu		      : 604r
clock		: 400MHz
revision	      : 49.2 (pvr 0009 3102)
bogomips	: 399.76
machine	: PReP MVME 3600 with MVME761
l2 cache	: none
simms		:

I did the following test on this machine afte which I decided that the L2
cache is not used.
I have a test program on VxWorks which takes about 110 ms for execution on
the MVME3604 with enable L2 cache
I ported this application to a RTAI module and did the test on linux and it
took about 420ms
So i disabled the L2 cache in VxWorks and did the test again and then it
took with VxWorks about 417ms.
After this and because of the content from /proc/cpuinfo I decided that the
L2 cache is not used.

BTW I am using kernel 2.4.25

Best regards,
Johannes

** Sent via the linuxppc-embedded mail list. See http://lists.linuxppc.org/

RE: No L2 Cache on PReP Machine

[Adrian Cox]

On Thu, 2004-08-19 at 10:04, Hager, Johannes, HRD/AB wrote:
> I have a test program on VxWorks which takes about 110 ms for execution on
> the MVME3604 with enable L2 cache
> I ported this application to a RTAI module and did the test on linux and it
> took about 420ms
> So i disabled the L2 cache in VxWorks and did the test again and then it
> took with VxWorks about 417ms.
> After this and because of the content from /proc/cpuinfo I decided that the
> L2 cache is not used.

That's very convincing.

If you have the source of your VxWorks BSP it may be worth looking for
code where VxWorks enables the L2 cache. You'll need to add a MVME3604
specific patch to your kernel to turn the cache on. I've just looked at
prep_setup.c, and there are already lots of board specific L2 handling
routines, but none for MVME3604.

- Adrian Cox
Humboldt Solutions Ltd.


** Sent via the linuxppc-embedded mail list. See http://lists.linuxppc.org/