Re: [Xenomai-core] Troubles with switchtest

[Gilles Chanteperdrix <gilles.chanteperdrix@xenomai.org>]

Jan Kiszka wrote:
> Gilles Chanteperdrix wrote:
>> Jan Kiszka wrote:
>>> Gilles Chanteperdrix wrote:
>>>> Jan Kiszka wrote:
>>>>> Hi Gilles,
>>>>>
>>>>> I'm currently facing a nasty effect with switchtest over latest git head
>>>>> (only tested this so far): running it inside my test VM (ie. with
>>>>> frequent excessive latencies) I get a stalled Linux timer IRQ quite
>>>>> quickly. System is otherwise still responsive, Xenomai timers are still
>>>>> being delivered, other Linux IRQs too. switchtest complained about
>>>>>
>>>>>     "Warning: Linux is compiled to use FPU in kernel-space."
>>>>>
>>>>> when it was started. Kernels are 2.6.28.9/ipipe-x86-2.2-07 and
>>>>> 2.6.29.3/ipipe-x86-2.3-01 (LTTng patched in, but unused), both show the
>>>>> same effect.
>>>>>
>>>>> Seen this before?
>>>> The warning about Linux being compiled to use FPU in kernel-space means
>>>> that you enabled soft RAID or compiled for K7, Geode, or any other
>>> RAID is on (ordinary server config).
>> By the way, I wonder how MMX accelerated software raid works on K7,
>> since the way I understand the code, calls to kernel_fpu_begin() can not
>> be nested.
>>
>> If you think they can be nested, then we can make switchtest test fpu in
>> Linux kernel-space when these options are enabled.
> 
> Sorry, I haven't looked that close into the in-kernel FPU handling so
> far. What users are nested in the standard kernel? Or is it RAID in itself?

RAID uses FPU. And on K7, basic things like clearing or copying user
pages, or even large memcpy do use FPU too. So, I would expect that when
enabling both, they could happen to be nested.

-- 
					    Gilles.