[Xenomai] xenomai , irq and pci

Gilles Chanteperdrix gilles.chanteperdrix at xenomai.org
Thu Mar 6 20:20:29 CET 2014


On 03/06/2014 09:25 AM, Johann Obermayr wrote:
> Am 05.03.2014 17:41, schrieb Gilles Chanteperdrix:
>> On 03/05/2014 05:22 PM, Johann Obermayr wrote:
>>> Hello,
>>>
>>> celeron dual core with PCIe - PCI bridge
>>> we use kernel 3.10.xx smp with  (isolcpus=0)
>>> smi is disabled.
>>> xenomai 2.6.3
>>>
>>> we have a pci card with a fpga (with irq) and sram.
>>>
>>> we have 2 task running.
>>>
>>> task0 is one high prior in primary domain on core0.
>>> this task wait for event, that is fired by fpga irq.
>>> than this task will make some pci accesses to the fpga.
>>>
>>> the other task (task1) is a shadow task, but running in secondary domain
>>> on core 1.
>>> This task make many big memcpy to sram.
>>>
>>> in the ipipe_handler_irq we have a function callback.
>>> a small driver hooks to this callback add make some tracepoint into
>>> a shared memory.
>>>
>>> with the trace we see some time a very high jitter in the ipipe_handler_irq
>>> function (around 250 us).
>>> has anyone an explanation for this?
>>>
>>> and a 4 byte access from task0 to fpga need more than 300us,
>>>    while task1 is writing to sram.
>> Maybe the problem is the size of the PCI burst when writing to the SRAM?
>> How large is it? If the sram is mapped with "write-combine", it will be
>> buffered and written in large bursts. Maybe you could try mapping the
>> sram area uncached?
>>
> Hi,
> 
> we use 2 real cores, no HT.
> task1 do a memcpy with 10000 bytes.

have you tried splitting the copy in smaller chunks, and use a mutex for 
exclusion between the two threads?

> 
> For mapping we use, rtdm_iomap_to_user
> rval = rtdm_iomap_to_user(user_info, lv.phys_addr, lv.len, PROT_READ | 
> PROT_WRITE, &lv.virt_addr, NULL, NULL);

You may want to try the following patch:

http://git.xenomai.org/xenomai-2.6.git/commit/?id=1b8fb14e486ac0604e44067a0f1f89dc14153e95



-- 
                                                                Gilles.




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