-----Original Message----- From: linu...@vger.kernel.org [mailto:linu...@vger.kernel.org] On Behalf Of Clark Williams Sent: Monday, April 13, 2009 7:44 PM To: Suresh Kumar SHUKLA Cc: 'rt-users' Subject: Re: Measuring timer interrupt latency

-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1

On Mon, 13 Apr 2009 12:14:42 +0530 Suresh Kumar SHUKLA <sure...@st.com> wrote:

Have you tried cyclictest? It's part of the rt-tests package that Thomas Gleixner wrote and that I now maintain.

You can pick up the latest tarball here:

http://www.kernel.org/pub/linux//kernel/people/clrkwllms/rt-tests/rt-tests-0 .35.tar.bz2

The thing is, I'm not sure how useful measuring the interval between interrupt and ISR. It's such a small component of the total latency value that it usually gets lost in the noise. Cyclictest measures the time between a timer fires and when the user-space program (cyclictest) actually gets to run after a sleep, which is the entire latency value. What you're talking about measuring on RT is basically a lookup and schedule() call, since all interrupts have threaded handlers on RT.

If you are wanting to decompose the latency into it's components on RT, I think you'd have:

1. ISR latency 2. Scheduler latency for IRQ thread 3. IRQ handler time 4. Scheduler latency for user-space thread

Cyclictest measures the aggregate of all these.

Clark -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.10 (GNU/Linux)

iEYEARECAAYFAknjSLEACgkQHyuj/+TTEp1kuACfSi13WaRt6nZDc53LXWqSsbsK Tv0AoJHpeXAjOkCPu5yBMElNDMr3Ij0y =5LIa -----END PGP SIGNATURE----- N '2flr8yzhXb2X,6G'vX^)^:{.nG+ 7% {1.[,z;"X^n r!v&zKkh(h-Z&"x.G+ih.(-i ]"j"z6m'ojdz9^ `~f#"7h'~m