Re: [pcp] systemtap/pcp integration

[David Smith <dsmith at redhat dot com>]

On 07/21/2014 08:32 PM, Nathan Scott wrote:
> Hi David,
> 
> ----- Original Message -----
>> [...]
>> Note that systemtap will create a file called 'mmv' in
>> /proc/systemtap/{MODULE_NAME}. I've just been using pcp's 'mmvdump'
>> utility to dump the contents of the /proc/systemtap/{MODULE_NAME}/mmv
>> file. Currently the pcp mmv pmda only looks in one place for mmv files,
>> but it might be possible to create a symbolic link to systemtap's mmv
>> file to make it happy.
> 
> (OOC, what's {MODULE_NAME} in this context?)

As Frank mentioned, {MODULE_NAME} is the name of the module, usually
autogenerated.

> A symlink would sorta work but it feels like a bit of a workaround - the
> PMDA is written to be able to detect arrival/departure of new MMV files
> based on changes in a directory (and the location of that directory is
> parameterised via /etc/pcp.conf variables).  I'd not recommend trying to
> find it within a stap script ... I imagine it will be cleaner if we go
> for separate user/kernel locations for MMV files.

The symlink feels like a bit of a workaround, because it *is* one. Long
term we certainly want a better way to find the systemtap MMV files.

> Attached patch (lightly tested) implements the PCP side of things with
> that in mind - with this patch (and making the kernel code manage the
> lifecycle of separate /proc/mmv/* entries), things should begin to work
> out-of-the-box (the MMV PMDA is already default-enabled in the default
> pmcd config file, so everything else is in place for you).

This code sounds like a step in the right direction.

Thanks.

-- 
David Smith
dsmith@redhat.com
Red Hat
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