Re: [RFC] [rt-tests] change to cyclictest behavior

Sven-Thorsten Dietrich
2010-01-12T17:00:09Z

On Wed, 2010-01-06 at 13:04 -0600, Clark Williams wrote:
> RT-ers,

Hi Clark,

sorry to be late to this, I have been out on a sailboat in the Bahamas.

When using the histogram feature, cyclictest already behaves the way you
describe below.

Sven

>
> 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