[lttng-dev] Is there a way to make LTTng use the same subbuffers for multiple processes?

[Amit Margalit]

This (current) behavior you describe is very suitable for our needs.

Is there an intention to insert a hook into setuid() in the future?
If yes - will the existing behavior remain as a default and the hook be 
used only if I choose to use it?

Thanks,

Amit Margalit
IBM XIV - Storage Reinvented
XIV-NAS Development Team
Tel. 03-689-7774
Fax. 03-689-7230



From:   Mathieu Desnoyers <mathieu.desnoyers at efficios.com>
To:     Amit Margalit/Israel/IBM at IBMIL
Cc:     Michel Dagenais <michel.dagenais at polymtl.ca>, 
lttng-dev at lists.lttng.org
Date:   04/29/2013 07:27 PM
Subject:        Re: [lttng-dev] Is there a way to make LTTng use the same 
subbuffers for multiple processes?



* Amit Margalit (AMITM at il.ibm.com) wrote:
> Another 2.2 question -
> 
> What if I have a single process, that forks, and each child process then 

> changes its own UID. Will the tracing continue on the parent UID 
buffers?

Yes, we indeed currently keep the user ID that was effective at process
creation or last exec() encountered, because we don't have hooks in
libc's setuid() at the moment.

Thanks,

Mathieu

> 
> Thanks,
> 
> Amit Margalit
> IBM XIV - Storage Reinvented
> XIV-NAS Development Team
> Tel. 03-689-7774
> Fax. 03-689-7230
> 
> 
> 
> From:   Michel Dagenais <michel.dagenais at polymtl.ca>
> To:     Amit Margalit/Israel/IBM at IBMIL
> Cc:     lttng-dev at lists.lttng.org
> Date:   04/29/2013 04:32 AM
> Subject:        Re: [lttng-dev] Is there a way to make LTTng use the 
same 
> subbuffers for multiple processes?
> 
> 
> 
> 
> > Our system is a 12-core x86 (6-core + HT). If I take 4 subbuffers of 
> 1MB, this means 4MB per
> > process. As the number of processes rises, this becomes prohibitive. 
> > For example, we may need to support > 500 sub-processes ==> 500 * 4MB 
= 
> 2GB - 
> > which is a bit too much.  Is there a way to tell LTTng to share the 
> sub-buffers with forked processes? 
> 
> This is the number one feature listed in the changelog for lttng-tools 
and 
> UST for version 2.2. The first release candidate is out so you can try 
the 
> feature, and the final 2.2 version should not be too far away.
> 
> http://lttng.org/lttng-tools-220-rc1
> - Add UST per UID buffers support
> 

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> lttng-dev mailing list
> lttng-dev at lists.lttng.org
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-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com


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