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Message-ID: <20100106130400.7f30ae55@torg>
Date: Wed, 6 Jan 2010 13:04:00 -0600
From: Clark Williams <williams@...hat.com>
To: RT <linux-rt-users@...r.kernel.org>
Cc: LKML <linux-kernel@...r.kernel.org>
Subject: [RFC] [rt-tests] change to cyclictest behavior
RT-ers,
I have a problem with the way cyclictest sets up measurement threads,
but before I went and changed things I thought I would ask if people
cherished this particular behavior.
Currently, when cyclictest is run with multiple threads (i.e. -t
option) it distributes both the sample interval and the realtime
priority by adding the 'distance' parameter to the interval and
decrementing the priority by one. This means if you have a distance of
500us (default), a specified RT priority of 95 and start four threads,
they will be started with the following parameters:
$ cyclictest -t4 -p95
Will give you:
thread priority sample interval
0 95 500
1 94 1000
2 93 1500
3 92 2000
What I'd like to do is modify this logic so that when '-a' (affinity) is
specified, the priority and sample interval will not be altered. I
don't think there's any point in distributing the priority's and
sample intervals when the measurement threads are pinned to their own
CPU.
So:
$ cyclictest -t4 -p95 -a
Would have each thread at SCHED_FIFO 95 and a sample interval of 500us.
Note that this behavior also occurs when the histogram (-h) option is
specified).
Thoughts?
Clark
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