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
Subject: Re: spi_async and heavy CPU occupation by ksoftirqd
Date: Thu, 09 Aug 2007 16:05:04 +0200 [thread overview]
Message-ID: <46BB1F10.3030608@dave-tech.it> (raw)
In-Reply-To: <200708080927.36737.david-b-yBeKhBN/0LDR7s880joybQ@public.gmane.org>
>> With the help of debug pin, I measured the execution time of
>> function work that is around 70us. Then I commented out the call of
>> spi_async and the ksoftirqd CPU occupation drops to 0%. Am I doing
>> something wrong?
>
> Are your transfers large enough to kick in DMA, or is it doing PIO?
I transfer just 1 byte every time the work is executed (HZ/10). I tried
to turn on and off DMA by setting/clearing enable_dma field but nothing
changed:
/* SPI Controller configuration */
static struct spi_imx_master spi_imx1_master_info = {
.num_chipselect = SPI_NUM_CHIPSELECT,
.enable_dma = 0
};
> At a first glance, I wonder if you're not spending too much time
> in the spi_imx "pump_transfers" tasklet. I have no idea how well
> tuned that driver is...
Hmmm ... how do you suggest me to investigate around this tasklet? Do I
need to use the toggling pin technique or does the kernel provides some
tools to do that? Could oprofile come to help?
> 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.
--
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:[~2007-08-09 14:05 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 [this message]
[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
[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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