Hi Clark, I already captured cyclictest (0.34) results. Thanks for new version info. It would be interesting to see the benefits of RT patch in ISR latency (#1) scenarios. Tim Sander's LMM seems perfectly suitable for this. regards, Suresh -----Original Message----- From: linux-rt-users-owner@xxxxxxxxxxxxxxx [mailto:linux-rt-users-owner@xxxxxxxxxxxxxxx] 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 <suresh.shukla@xxxxxx> wrote: > Hi, > > I want to profile the improvements in interrupt latency with and > without RT patches. > > The approach I have in mind is that time gap between IRQ firing and > IRQ handler reading value of counter would be sufficient to reveal the > interrupt latency. These values can be analysed for min/max/avg. > > Is there any test program which captures interrupt latency (for x86) ? > I checked realfeel but it is user mode program and am not sure of its > accuracy. > > regards, > Suresh > 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 -- To unsubscribe from this list: send the line "unsubscribe linux-rt-users" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
