RE: no access to local variables in function

["Lentes, Bernd" <bernd dot lentes at helmholtz-muenchen dot de>]

Bernd wrote:

> -----Original Message-----
> From: systemtap-owner@sourceware.org [mailto:systemtap-
> owner@sourceware.org] On Behalf Of Lentes, Bernd
> Sent: Thursday, May 28, 2015 2:07 PM
> To: 'systemtap@sourceware.org'
> Subject: no access to local variables in function
>
> Hi,
>
> i'm new to systemtap. I try to check some local variables of kernel
> functions. I have a SLES 10 SP4, kernel 2.6.16.60-0.103.1-smp. I'm using
> systemtap 0.8.
> I'm following the instructions from
> https://sourceware.org/systemtap/SystemTap_Beginners_Guide/target
> variables.html .
>
> If I try to use the example from this page I get:
> idcc-devel:~/systemtap # stap -L 'kernel.function("vfs_read")'
> kernel.function("vfs_read@fs/read_write.c:248")
>
> Checking other functions with local variables also does not work:
> idcc-devel:~/systemtap # stap -L 'kernel.function("local_bh_enable")'
> kernel.function("local_bh_enable@kernel/softirq.c:139")
>
> idcc-devel:~/systemtap # stap -L 'kernel.function("__tasklet_schedule")'
> kernel.function("__tasklet_schedule@kernel/softirq.c:224")
>
> idcc-devel:~/systemtap # stap -L
> 'kernel.function("tasklet_kill_immediate")'
> kernel.function("tasklet_kill_immediate@kernel/softirq.c:439")
>
> I don't see any local variable. What can I do ?
>
> Btw: is there a chance to monitor the variables of a blacklisted function ?

Maybe it's an idea to use $$vars, $$parms ...
But I don't know how to interpret this:

$$vars: t=0xffff81003ead2d68    $$parms: t=0xffff81003ead2d68   $$locals:

My problem is that I have constant between 5 and 15% si load on that machine (Soft Interrupt). But I don't know the reason.
Maybe probe::softirq.entry is helpful but I don't know how to use it.

Thanks for any help.


Bernd

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