Re: 2.6.19-rc6-rt5

Robert Schwebel
2006-11-22T11:38:00Z

On Mon, Nov 20, 2006 at 11:02:30PM +0100, Ingo Molnar wrote:
> i've released the 2.6.19-rc6-rt5 tree, which can be downloaded from the
> usual place:

[...]

> as usual, bugreports, fixes and suggestions are welcome,

I have problems runinng cyclictest on the more recent -rt kernels. A
similar problem I reported recently on a Pentium M / ICH6 Dell box is
solved by using the acpi_pm timer.

The problematic box is a 700 MHz Celeron (Coppermine) which doesn't have
ACPI.

The last kernel that run with sane cyclictest results was 2.6.18-rt6:

- root@krachkiste:~/cyclictest-v0.11 ./cyclictest -n -t 4 -p 90 -l 10000
0.13 0.10 0.13 1/52 2721

T: 0 ( 2718) P:90 I: 1000 C: 10000 Min: 14 Act: 47 Avg: 52 Max: 170
T: 1 ( 2719) P:89 I: 1500 C: 6667 Min: 16 Act: 22 Avg: 45 Max: 138
T: 2 ( 2720) P:88 I: 2000 C: 5001 Min: 16 Act: 35 Avg: 44 Max: 101
T: 3 ( 2721) P:87 I: 2500 C: 4001 Min: 14 Act: 28 Avg: 38 Max: 114

The following numbers have been taken on 2.6.19-rc6-rt5, the effect is there
since 2.6.18-rt7.

- "cyclictest -n -p 90 -t 4" is just "running upwards".

root@krachkiste:~/cyclictest-v0.11 ./cyclictest -n -p 90 -t 4 -l 1000
0.00 0.00 0.00 1/54 2843

T: 0 ( 2840) P:90 I: 1000 C: 1000 Min: 7294 Act: 3008486 Avg: 1508852 Max: 3008486
T: 1 ( 2841) P:89 I: 1500 C: 1000 Min: 7195 Act: 2508885 Avg: 1258994 Max: 2508885
T: 2 ( 2842) P:88 I: 2000 C: 1000 Min: 7188 Act: 2009375 Avg: 1009235 Max: 2009375
T: 3 ( 2843) P:87 I: 2500 C: 1000 Min: 7184 Act: 1509868 Avg: 759479 Max: 1509868

- Using a relative timer (-r), I get huge latencies:

root@krachkiste:~/cyclictest-v0.11 ./cyclictest -n -p 90 -t 4 -r -l 1000
0.00 0.00 0.00 1/56 2838

T: 0 ( 2835) P:90 I: 1000 C: 1000 Min: 742 Act: 6937 Avg: 6952 Max: 9214
T: 1 ( 2836) P:89 I: 1500 C: 1000 Min: 244 Act: 6424 Avg: 6454 Max: 8718
T: 2 ( 2837) P:88 I: 2000 C: 999 Min: 1288 Act: 5910 Avg: 5962 Max: 8216
T: 3 ( 2838) P:87 I: 2500 C: 999 Min: 778 Act: 5409 Avg: 5462 Max: 7713

This is with "lapic lapictimer" on the kernel commandline.

The system has chosen "pit" as it's clocksource, switching to tsc or jiffies
doesn't change anything.

With 2.6.18-rt6 I've seen these lines in the dmesg output:

Nov 22 12:05:24 krachkiste kernel: Time: tsc clocksource has been installed.
Nov 22 12:05:24 krachkiste kernel: Event source pit disabled
Nov 22 12:05:24 krachkiste kernel: Event source lapic configured with caps set: 08
Nov 22 12:05:24 krachkiste kernel: hrtimers: Switched to high resolution mode CPU 0

Especially the "Switched to high resolution mode" isn't there with the later
kernels (high resolution timers is on in the config, dyntick is off).

Robert
--
Dipl.-Ing. Robert Schwebel | http://www.pengutronix.de
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