Messages in this thread | | | Subject | RE: 2.6.11, IDE: Strange scheduling behaviour: high-pri RT process not scheduled? | Date | Thu, 31 Mar 2005 17:19:04 +0200 | From | "kus Kusche Klaus" <> |
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> getting /dev/rtc handling right for latency measurement is > ... tricky. > The method i'm using under PREEMPT_RT is: > > chrt -f 84 -p `pidof 'IRQ 0'` > chrt -f 95 -p `pidof 'IRQ 8'` > ./rtc_wakeup -f 1024 -t 100000
I tried it your way.
First impressions with realtime-preempt-2.6.12-rc1-V0.7.42-01, rtc_wakeup and chrt:
The main difference is not between rtc_wakeup and my test script (the timings agree very well), but comes from chrt for 'IRQ 8':
System not loaded, original 'IRQ 8' prio 49: * rtc_wakeup at 89(99): max jitter: 378.2% (461 usec), missed irqs: 0 * rtc_wakeup at 1(11): max jitter: 97.1% (118 usec), missed irqs: 25 System not loaded, 'IRQ 8' prio at 95: * rtc_wakeup at 89(99): max jitter: 19.1% ( 23 usec), missed irqs: 0 * rtc_wakeup at 1(11): max jitter: 190.7% (232 usec), missed irqs: 52
The following tests are made with 'IRQ 8' at 95, rtc_wakeup at 89(99): * Heavy mmap load, no oom: max jitter: 42.1% ( 51 usec) * Heavy mmap load, oom: max jitter: 11989.2% (14635 usec) (but still "missed irqs: 0", so IRQ 8 was also blocked for 14 ms) * USB reads, no error: max jitter: 707.7% ( 863 usec) (happens rarely) * USB reads, error: max jitter: 7247.2% ( 8846 usec) (again, no missed irqs) * USB stick connect: max jitter: 5776.7% ( 7051 usec) * USB stick disconnect: max jitter: 2966.6% ( 3621 usec) (both without error!)
Notes: * My system does not have a 'IRQ 0' kernel thread. It has IRQ 1, 3, 7, 8, 12 and 14. This is strange, because /proc/interrupts says 0: 4805658 XT-PIC timer 0/5658 2: 0 XT-PIC cascade 0/0 3: 0 XT-PIC serial 0/0 7: 17538 XT-PIC uhci_hcd:usb1, eth0 0/17538 8: 838523 XT-PIC rtc 0/38523 14: 5775 XT-PIC ide0 0/5775 * The syntax of chrt has changed: chrt -f -p <prio> <pid> * I run rtc_wakeup with -f 8192. This is more realistic in our case.
CF card (IDE) load does not hurt as long as the rtc test runs with a very high rtpri: The results did not differ significantly from no-load results. Attempts with tracing on and results with running the test at low rtpri will follow tomorrow...
-- Klaus Kusche Entwicklung Software - Steuerung Software Development - Control
KEBA AG A-4041 Linz Gewerbepark Urfahr Tel +43 / 732 / 7090-3120 Fax +43 / 732 / 7090-8919 E-Mail: kus@keba.com www.keba.com - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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