Messages in this thread | | | Date | Mon, 28 Jan 2008 16:11:29 +0100 | From | Luotao Fu <> | Subject | Re: 2.6.24-rc8-rt1: Strange latencies on mpc5200 powerpc |
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Hi,
I took some time today and went through Wolfgangs scenarios partly. Now some results from my side. I ran my tests on a 2.6.24-rt1
Wolfgang Grandegger wrote: > I also did some more measurements and made, by chance, interesting > observations. I will summarize in more detail later on. Here are some > preliminary results. My high latencies of up to 570us (without latency > tracer) seem to be caused mainly by the following setting: > > CONFIG_RCU_TRACE=m >
I also got high latencies without CONFIG_RCU_TRACE set at all. setting CONFIG_RCU_TRACE to y or m causes also high latency though in my test runs. Hence I doubt the rcu Tracer is really the problem.
As I mentioned in my last mail. Only thing I could reproduce reliably is that the measurement results depend heavily on kind of the non-rt Workload. For with hackbench or cache calibrator I couldn't produce abnormal high latencies. Nor could I produce the hight latencies on a system booted via flash. Hence my suspects stays on the fec irq thread and filesystem access routines.
> With CONFIG_NO_HZ=y or CONFIG_PPC_BESTCOMM_GEN_BD=y the latency > increases by approx. 100..150us, each. >
Since I was producing high latencies independently from the rcu settings. I didn't spend a lot of time playing around with the GEN_BD and dynamic clock. All I can say is that disabling them also cause high latency. ;-) The average results don't differ significantly in my test runs.
cheers Luotao Fu -- Dipl.-Ing. Luotao Fu | Phone: +49-5121-206917-3 Pengutronix - Linux Solutions for Science and Industry Entwicklungszentrum Nord http://www.pengutronix.de
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