On 2011-08-26 22:42, George Broz wrote: > Hello, > > I'm experiencing very large overruns in the neighborhood of 10 to 50 > *milli-seconds* as reported by the Xenomai latency tool in user-task mode > whenever the Linux OS is heavily loaded. Under lighter loads these are in > the 30 to 70 micro-second (normal) range. > > My system is: > - Linux 2.6.37.6 (32-bit), Ubuntu 10.10 distribution > - Xenomai 2.5.6 using I-pipe patch adeos-ipipe-2.6.37.6-x86-2.9-02 > - Intel x86 Atom (dual-core) CPU D510 @ 1.66GHz > - Emb. dev board from Intel (ICH8M ctrlr, Ethernet h/w for e1000e) > - Xenomai configured w&w/o --enable-smp --enable-x86-tsc options > - gcc version 4.4.5 > > I've followed all of the recommendations for kernel configuration and have > disabled CPU sleep features in the BIOS such as SpeedStep and C-States. > Legacy USB has been disabled in the BIOS. Hyperthreading has also been > disabled, although I don't think it matters. > > The heavy load was to compile a new Linux kernel while the latency test > ran. > > I've captured several traces with the I-pipe tracer - here are some of the > milli-second overrun excerpts: > > snippet: > Type User Val. Time Delay Function (Parent) > :| +begin 0x80000001 -14384 0.551 __ipipe_handle_exception+0x3d3 > (error_code+0x5f) > :| +end 0x80000001 -14383! 14344.649 __ipipe_handle_exception+0x2d9 > (error_code+0x5f) > :| +begin 0xffffff02 -39 0.995 reschedule_interrupt+0x30 > (<40116e89>) > > snippet: > : +func -17242 0.545 _raw_spin_lock+0x3 (ipc_lock+0x2e) > : +func -17241! 17188.986 ipcperms+0x10 > (sys_semtimedop+0x2f8) > :| +begin 0xffffff09 -52 0.797 ipipe_ipi3+0x30 > (sys_semtimedop+0x396) > :| +func -51 0.701 __ipipe_handle_irq+0xa > (ipipe_ipi3+0x37) > > snippet: > : #func -39426 0.605 scheduler_tick+0xa > (update_process_times+0x5d) > : #func -39425 0.797 ktime_get+0xa > (sched_clock_tick+0x5a) > : #func -39424! 39377.690 acpi_pm_read+0x3 (ktime_get+0x6a) > :| #begin 0xffffff09 -47 0.923 ipipe_ipi3+0x30 (acpi_pm_read+0xf) > :| #func -46 0.707 __ipipe_handle_irq+0xa > (ipipe_ipi3+0x37)
Specifically this last snippet suggests that your hardware has some serious latency problems. There is nothing in that code path that allows a software explanation of those 39 ms. Jan -- Siemens AG, Corporate Technology, CT T DE IT 1 Corporate Competence Center Embedded Linux _______________________________________________ Xenomai-help mailing list [email protected] https://mail.gna.org/listinfo/xenomai-help
