[lttng-dev] Limitations on subbuf_size / num_subbuf?

[David Goulet]

Alexandre Montplaisir:
> On 13-04-18 01:11 PM, Mathieu Desnoyers wrote:
>> * Mathieu Desnoyers (mathieu.desnoyers at efficios.com) wrote:
>>> * Alexandre Montplaisir (alexmonthy at voxpopuli.im) wrote:
>>>> On 13-04-18 02:11 AM, Amit Margalit wrote:
>>>>> Hi,
>>>>>
>>>>> Thank for the quick response. Here is the missing data:
>>>>>
>>>>> UST
>>>>> 2.6.32.12-205 (I had to make a tiny patch to make it compile)
>>>>> MemTotal:       24628852 kB
>>>>> lttng-ust-2.1.2
>>>>> lttng-tools-2.1.1
>>>>> lttng-modules-2.1.1
>>>>> babeltrace-1.1.0
>>>>> userspace-rcu-0.7.6
>>>>>
>>>>> Which patch for 4MB?
>>>> Hi,
>>>>
>>>> Not sure if it's specifically this one that Matthew was talking about,
>>>> but we have such a patch in the PPA packages. See:
>>>> http://bazaar.launchpad.net/~lttng/lttng-tools/packaging-daily/view/head:/patches/0002-Increase-default-subbuffer-size-to-4MB.patch
>>> First, it should be noted that lttng enable-channel allow overriding the
>>> subbuffer size.
>>>
>>> It should be noted that lttng-modules 2.2 is going to output even _more_
>>> events, so I don't think just making the buffers larger by default is
>>> the right approach.
>> Oh, and I notice that the PPA changes the UST default to 4MB per
>> subbuffer too.
>>
>> That's not going to be pretty for per-pid tracing (which is the default)
>> on a system with 16 CPUs, tracing 100 processes with UST. 4x4MBx16x100 =
>> 25600 MB (25GB) of buffers just for UST.
> 
> Ok good to know, we will have to update it then.
> 
>> Messing with defaults in packaging seems odd.
> 
> Actually, it's a pretty common practice ;)

Well... maybe but at least *please* inform the maintainers when you do
that because when bugs are received, it is pretty important for us (at
least for me) to know what are the difference(s) between the dev tree
and what is actually in production.

Thanks!
David

> 
> 
> Cheers,
> Alex
> 
>>
>> Mathieu
>>
>>> I think we need to port the "loglevel" from UST to lttng-modules ASAP,
>>> and assign a "debug" loglevel to events we don't care about by default.
>>>
>>> Thoughts ?
>>>
>>> Thanks,
>>>
>>> Mathieu
>>>
>>>>> Thanks,
>>>>>
>>>>> Amit Margalit
>>>>> IBM XIV - Storage Reinvented
>>>>> XIV-NAS Development Team
>>>>> Tel. 03-689-7774
>>>>> Fax. 03-689-7230
>>>>>
>>>>>
>>>>>
>>>>> From:   Matthew Khouzam <matthew.khouzam at ericsson.com>
>>>>> To:     <lttng-dev at lists.lttng.org>
>>>>> Date:   04/15/2013 05:24 PM
>>>>> Subject:        Re: [lttng-dev] Limitations on subbuf_size / num_subbuf?
>>>>>
>>>>>
>>>>>
>>>>> Not at all a n00b question, but could you give some more info? what is 
>>>>> your version of LTTng tools, are you using UST or kernel tracing? How much 
>>>>> ram is on your system? Kernel version? 
>>>>>
>>>>> I actually have the patched lttng that has standard subbuffer sizes of 4 
>>>>> mb, so I have not personnaly seen that problem. But the first thing I 
>>>>> would do is upgrade to the latest stable.
>>>>>
>>>>> On 13-04-14 06:49 AM, Amit Margalit wrote:
>>>>> Hello, 
>>>>>
>>>>> Sorry for the noob question. I seem to be unable to define the total of 
>>>>> subbuf_size * num_subbuf higher than 4MB. I am getting ~30% discarded 
>>>>> tracepoint data. 
>>>>>
>>>>> Any assistance would be greatly appreciated. 
>>>>>
>>>>> Amit Margalit 
>>>>> IBM XIV - Storage Reinvented 
>>>>> XIV-NAS Development Team 
>>>>> Tel. 03-689-7774 
>>>>> Fax. 03-689-7230 
>>>>
>>>> _______________________________________________
>>>> lttng-dev mailing list
>>>> lttng-dev at lists.lttng.org
>>>> http://lists.lttng.org/cgi-bin/mailman/listinfo/lttng-dev
>>> -- 
>>> Mathieu Desnoyers
>>> EfficiOS Inc.
>>> http://www.efficios.com
>>>
>>> _______________________________________________
>>> lttng-dev mailing list
>>> lttng-dev at lists.lttng.org
>>> http://lists.lttng.org/cgi-bin/mailman/listinfo/lttng-dev
> 
> 
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