Re: Experiences with Debian Sarge on MPC8xx ?

Dear Raphael,

in message [ref] you wrote:

Debian GNU/Linux v3.1 (Sarge) is out so give it a try on my MPC850
running Debian v3.0 for more then 1 year with Denx's 2.4.20 kernel.

It failed with more or less the same reason as described May 2004
in this posting 
http://lists.debian.org/debian-embedded/2004/05/msg00032.html

Things changed since May 2004 but the problem seams to be. I'm using
100% binary compatible Debian GNU/Linux 3.0 (Woody) without any
problems on my MPC860 board with kernel FPU emulation enabled. This
math-emu implementation seams to be stable enought to work with libc6
2.2.5 and very many server application and large C++ application at high
load (our stress tests are really horrible for the compleate system!).

I guess you are aware that the FPU emulation is a  nightmare  perfor-
mance-wise  -  you  take  a  kernel  exception  for each and every FP
instruction. FP execution is  several  orders  faster  when  you  use
soft-float  (which,  of  course,  requires  all soft-float libraries,
too).

I've also heard from people on IRC that 100% Sarge works for them on
FPU-less MPC boards without trouble. So while I'm investigating the
problem would like to hear some more respond on this issue from
people who spend more time on getting Sarge running with 100% Debian
v3.1 (Sarge) on their MPC8xx environment.

This is probably not a FP issue but may be related to the cache  line
size  and/or  the  infamous  "dcbz"  misbehaviour.  The  standard fix
(removing memset.S when building glibc) has been discussed many times
before; see for example the patches / build scripts for  our  EDK  or
Dan Kegel's crosstool.

The -msoft-float advice is not what I'm looking for. I'm not sure if
the FPU is responsible for the problem. Maybe the Debian libc6 2.3.2
package is missing something important for the MPC8xx PowerPC (the
cache-line-size is 4 for Debian's libc on PowerPC by default). The

4 what? Bytes? 

big advantage using a standard distribution is the big number of
precompiled packages. I do not intent to recompile more then 18000
due to this first failed tests.

You don't intend to use 18000 packages on your embedded system either
;-)

Best regards,

Wolfgang Denk

-- 
Software Engineering:  Embedded and Realtime Systems,  Embedded Linux
Phone: (+49)-8142-66989-10 Fax: (+49)-8142-66989-80 Email: wd@denx.de
"Free markets select for winning solutions."        - Eric S. Raymond