Re: [RFC 0/4] Improving SPI driver latency (vs v3.8.13.14-rt31)

["Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>]

Hello Jeff,

On Mon, Sep 01, 2014 at 09:30:31AM -0500, Jeff Epler wrote:
> Unfortunately, I found that there were frequent large latencies, some
> over 10ms, when using /dev/spidev.  This seems to be typical of others'
> experience using it (for instance, one can find threads discussing
> disappointing RT performance of SPI on the beaglebone and pandaboard; at
> least one raspberry pi project chose to implement a pure userspace SPI
> driver instead of using spidev)
> 
> At all levels of the SPI stack, I found things that could be improved if
> lowest delays are the goal.  I doubt that in their current form these
> changes are suitable to be incorporated in preempt-rt, but I hope that 
> this might spur some discussion that would ultimately lead to better
> realtime performance of SPI in the preempt-rt kernel.
I wonder why you didn't consider mainline as target for your patches
instead of preempt-rt. Also you might want to cc the spi maintainer on
this topic. I didn't check in detail what you did, but if it's useful
for others it would be a pity if it were not picked up because the
responsible people were not aware of your effort.

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |
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