From: "Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>
To: Jeff Epler <jepler@unpythonic.net>
Cc: linux-rt-users@vger.kernel.org
Subject: Re: [RFC 0/4] Improving SPI driver latency (vs v3.8.13.14-rt31)
Date: Tue, 9 Sep 2014 22:01:17 +0200 [thread overview]
Message-ID: <20140909200117.GU23009@pengutronix.de> (raw)
In-Reply-To: <1409581835-70814-1-git-send-email-jepler@unpythonic.net>
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
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Pengutronix e.K. | Uwe Kleine-König |
Industrial Linux Solutions | http://www.pengutronix.de/ |
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prev parent reply other threads:[~2014-09-09 20:01 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-09-01 14:30 [RFC 0/4] Improving SPI driver latency (vs v3.8.13.14-rt31) Jeff Epler
2014-09-01 14:30 ` [PATCH 1/4] spi: reenable sync SPI transfers Jeff Epler
2014-09-01 14:30 ` [PATCH 2/4] spidev: Avoid runtime memory allocations Jeff Epler
2014-09-01 14:30 ` [PATCH 3/4] spidev: actually use synchronous transfers Jeff Epler
2014-09-01 14:30 ` [PATCH 4/4] spidev-s3c64xx: allocate dma channel at startup Jeff Epler
2014-09-01 15:41 ` [RFC 0/4] Improving SPI driver latency (vs v3.8.13.14-rt31) Philipp Lutz
2014-09-01 18:13 ` Jeff Epler
2014-09-01 22:30 ` Harry van Haaren
2014-09-09 20:01 ` Uwe Kleine-König [this message]
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