Gilles Chanteperdrix wrote:
> 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.
> 

I think the trick against /this/ is preempt_disable/enable in
kernel_fpu/begin/end. But that won't work for Xenomai, of course.

Jan

-- 
Siemens AG, Corporate Technology, CT SE 2
Corporate Competence Center Embedded Linux

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