New subject: [Bug 732980] Loading module mISDN_dsp makes ksoftirqd use high % of CPU time

28 Nov 2011

      https://bugzilla.novell.com/show_bug.cgi?id=732980

https://bugzilla.novell.com/show_bug.cgi?id=732980#c0

           Summary: Loading module mISDN_dsp makes ksoftirqd use high % of
                    CPU time
    Classification: openSUSE
           Product: openSUSE 12.1
           Version: Final
          Platform: x86-64
        OS/Version: SuSE Other
            Status: NEW
          Severity: Normal
          Priority: P5 - None
         Component: Kernel
        AssignedTo: kernel-maintainers@forge.provo.novell.com
        ReportedBy: claude.diderich@yahoo.com
         QAContact: qa@suse.de
          Found By: ---
           Blocker: ---

User-Agent:       Mozilla/5.0 (Windows NT 6.1; WOW64; rv:8.0) Gecko/20100101
Firefox/8.0

When loading the ISDN modules mISDN_core and then mISDN_dsp into the kernel
using modprobe, the soft irq handler ksoftirqd usses high % of CPU time on one
core of the processor(s) installed in the system.

PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND
10 root      20   0     0    0    0 S   47  0.0   1:53.77 ksoftirqd/1

Unloading the module mISDN_dsp from the kernel, makes the usage diappear again.

Issue has been reproduced on two different machines under openSUSE 12.1 with
different hardware (one with ISDN adapter and one without).

Kernel is
Linux joshua 3.1.0-1.2-default #1 SMP Thu Nov 3 14:45:45 UTC 2011 (187dde0)
x86_64 x86_64 x86_64 GNU/Linux

dmesg shows
Modular ISDN core version 1.1.21
NET: Registered protocol family 34
DSP modul 2.0
mISDN_dsp: DSP clocks every 64 samples. This equals 2 jiffies.

Reproducible: Always

Steps to Reproduce:
1. modprobe mISDN_core
2. modprobe mISDN_dsp
3. Watch CPU usage, for example through top

Actual Results:  
Machine spends lot of time in ksoftirqd

PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND
10 root      20   0     0    0    0 S   47  0.0   1:53.77 ksoftirqd/1

Expected Results:  
Machine spends no time in ksoftirqd (result shown after unloading mISDN_dsp and
mISDN_core)

PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND
10 root      20   0     0    0    0 S   0  0.0   3:03.77 ksoftirqd/1

ISDN functionality is not affected (at least none could be identified).

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[Bug 732980] New: Loading module mISDN_dsp makes ksoftirqd use high % of CPU time

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