From: llandre <r&d2-4VKA1VU3ct/j+vYz1yj4TQ@public.gmane.org>
To: David Brownell <david-b-yBeKhBN/0LDR7s880joybQ@public.gmane.org>
Cc: spi-devel-general-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org,
Andrea Paterniani
<a.paterniani-03BXCEkGbFHYGGNLXY5/rw@public.gmane.org>
Subject: Re: spi_async and heavy CPU occupation by ksoftirqd
Date: Fri, 10 Aug 2007 10:52:02 +0200 [thread overview]
Message-ID: <46BC2732.5070504@dave-tech.it> (raw)
In-Reply-To: <200708090823.29708.david-b-yBeKhBN/0LDR7s880joybQ@public.gmane.org>
> That seems to be the most precise tool you have, unless you
> have access to the JTAG-style hardware tools giving access
> to the on-chip instruction trace buffers found in many ARMs.
Unfortunatley trace port is not available so I have to use the old
fashioned debug pin technique.
>> or does the kernel provides some
>> tools to do that? Could oprofile come to help?
>
> Statistical profiling probably wouldn't help. I'm not sure that
> anything like gprof is working in the kernel. Folk that I know
> have done that level analysis tend to rely on hardware trace tools.
I see.
>>> I'd expect that using spi_sync() wouldn't save much, but it might
>>> be worth verifying that.
>> Initially my driver used spi_sync. When I realized the huge CPU
>> occupation I modified it in order to use spi_async instead but, again,
>> nothing changed.
>
> And that should have been a HUGE clue that the way you were calling
> it wasn't a factor at all.
I moved the set/clear pin functions inside the iMXL master driver and I
found the problem is at line 804 inside the interrupt handler:
qt510_debug_pin(1);
while ((read(drv_data) == 0) && limit--);
qt510_debug_pin(0);
Usually the high pulse lasts about 10ms. Occasionally (about 1 time out
of 3) it lasts about 300 ms ! That would explain the ksoftirqd abnormal
CPU occupation.
I hope Andrea can come to help.
--
llandre
DAVE Electronics System House - R&D Department
web: http://www.dave-tech.it
email: r&d2-4VKA1VU3ct/j+vYz1yj4TQ@public.gmane.org
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next prev parent reply other threads:[~2007-08-10 8:52 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-08-08 8:21 spi_async and heavy CPU occupation by ksoftirqd llandre
[not found] ` <46B97D01.5000208-4VKA1VU3ct/j+vYz1yj4TQ@public.gmane.org>
2007-08-08 16:27 ` David Brownell
[not found] ` <200708080927.36737.david-b-yBeKhBN/0LDR7s880joybQ@public.gmane.org>
2007-08-09 14:05 ` llandre
[not found] ` <46BB1F10.3030608-4VKA1VU3ct/j+vYz1yj4TQ@public.gmane.org>
2007-08-09 15:23 ` David Brownell
[not found] ` <200708090823.29708.david-b-yBeKhBN/0LDR7s880joybQ@public.gmane.org>
2007-08-10 8:52 ` llandre [this message]
[not found] ` <46BC2732.5070504-4VKA1VU3ct/j+vYz1yj4TQ@public.gmane.org>
2007-08-10 10:29 ` Andrea Paterniani
[not found] ` <FLEPLOLKEPNLMHOILNHPMEKGDKAA.a.paterniani-03BXCEkGbFHYGGNLXY5/rw@public.gmane.org>
2007-08-10 11:32 ` llandre
[not found] ` <46BC4CD3.5090304-4VKA1VU3ct/j+vYz1yj4TQ@public.gmane.org>
2007-08-10 12:27 ` R: " Andrea Paterniani
[not found] ` <FLEPLOLKEPNLMHOILNHPIEKIDKAA.a.paterniani-03BXCEkGbFHYGGNLXY5/rw@public.gmane.org>
2007-08-14 8:29 ` llandre
[not found] ` <46C167F0.4040100-4VKA1VU3ct/j+vYz1yj4TQ@public.gmane.org>
2007-08-14 9:43 ` llandre
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