From: Simon Thelen <urday@student.kit.edu>
To: <linux-rt-users@vger.kernel.org>
Subject: Low USB polling frequency with RT-PREEMPT
Date: Tue, 5 Sep 2017 17:05:39 +0200 [thread overview]
Message-ID: <20170905150539.GF2607@anonymous> (raw)
Hello,
We have some Dynamixel robitic actuators hooked up via USB to an Ubuntu
14.04 system running the 4.4.79-rt92 kernel. When using a kernel built
without the realtime patches (CONFIG_PREEMPT not set) we can query the
bus at 1000Hz (2 devices at 500Hz each) whereas with the realtime kernel
(CONFIG_PREEMPT=y, CONFIG_PREEMPT_RT_FULL=y) we only get 62.5Hz per
device. The USB device requests Ivl=0ms in both cases and the issue
isn't related to load etc. The polling rate is always 62.5Hz (It takes
~15ms for every read()).
Is this a known limitation of USB with the CONFIG_PREEMPT_RT patches and
is there any method to improve the polling rate?
--
Simon Thelen
next reply other threads:[~2017-09-05 15:24 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-09-05 15:05 Simon Thelen [this message]
2017-09-05 17:53 ` Low USB polling frequency with RT-PREEMPT Niels Kolthoff
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