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Re:

To: Manuel Lauss <manuel.lauss@googlemail.com>
Subject: Re:
From: David Daney <ddaney@caviumnetworks.com>
Date: Fri, 11 Jun 2010 10:06:50 -0700
Cc: Jabir M <Jabir_M@pmc-sierra.com>, linux-mips@linux-mips.org, ralf@linux-mips.org
In-reply-to: <AANLkTimHTt3jCTPrlIDAkdDc8WheBf7bdEThk3JO8yNO@mail.gmail.com>
References: <BE430C874DBA6841A75E65151DCC6E1C0407668F@BBY1EXM11.pmc_nt.nt.pmc-sierra.bc.ca> <AANLkTimHTt3jCTPrlIDAkdDc8WheBf7bdEThk3JO8yNO@mail.gmail.com>
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On 06/11/2010 07:32 AM, Manuel Lauss wrote:
Hi,

On Fri, Jun 11, 2010 at 4:06 PM, Jabir M<Jabir_M@pmc-sierra.com>  wrote:
    I am working on a FPU-less 34k MIPS platform with linux-2.6.24
kernel. After running a Darwin media streaming server on the board
for a while, my oprofile results shows high utilization on
fpu_emulator_cop1Handler()&  r4k_wait().


r4k_wait() is the idle task, so that indicates there is nothing to do at those sample points.

wiki page http://www.linux-mips.org/wiki/Floating_point says gcc will
use hard float as default and soft float is best suited model for a
fpu less processor.  Could anyone kindly help me in understanding use
of -msoft-float .
Whether I need to compile

1. kernel with -msoft-float ? or

The kernel doesn't use floating point.  So it doesn't matter.

2. Glibc ? or
3. Application ? or
4. All the above ?


If you don't want to use the kernel's FP emulator, you need 2 and 3.


I have fought with this in the past; what you need to do is:
- build gcc with softfloat support (mipsel-softfloat-linux-gnu triplet
for example),
- build a libc with this new compiler,
- then rebuild all libraries and apps with you new softfloat toolchain.

<plug>
I have a working softfloat environment for MIPS32 here at [1], it includes a
complete c/c++ toolchain with gcc-4.4.3.   It's built for mips32r1, no idea if
it is supposed to work with 34k cores.
</plug>

34k is mips32r2, which will run r1 code with no problem.


Best regards,
         Manuel Lauss

[1]  http://mlau.at/files/mips32-linux/




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