From: Jeff Epler <jepler@unpythonic.net>
To: Philipp Lutz <philipp.lutz@dlr.de>
Cc: linux-rt-users@vger.kernel.org
Subject: Re: [RFC 0/4] Improving SPI driver latency (vs v3.8.13.14-rt31)
Date: Mon, 1 Sep 2014 13:13:28 -0500 [thread overview]
Message-ID: <20140901181328.GB81857@unpythonic.net> (raw)
In-Reply-To: <540493AA.2020207@dlr.de>
On Mon, Sep 01, 2014 at 05:41:30PM +0200, Philipp Lutz wrote:
> Have you looked into setting a RTPRIO for the SPI worker threads
> (spi_init_queue() in spi.c)? As far as I see hardly any SPI
> hardware-dependent driver sets the "rt" property in the respective
> spi_master struct, so that the main SPI driver (spi.c) will not use a RT
> priority, which will be MAX_RT_PRIO - 1.
Sort of.
I was unaware of the "rt" property so I never tried setting it on the
kernel side. However, I did run into the idea of using "chrt" on the
kernel tasks [spi1] and [irq/99-spi-s3c6]. This improved things
somewhat, but this plus eliminating DMA acquistion still left me with
some 800+us latencies that I didn't want.
(it may have also helped somewhat to to use cpuset to bind these tasks
to the same CPU where my realtime task runs--the U3 is a 4-core chip,
and linuxcnc binds to the last CPU by default)
Jeff
next prev parent reply other threads:[~2014-09-01 18:13 UTC|newest]
Thread overview: 10+ 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 [this message]
2014-09-01 22:30 ` Harry van Haaren
2014-09-09 20:01 ` Uwe Kleine-König
-- strict thread matches above, loose matches on Subject: below --
2014-09-14 14:45 Jeff Epler
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