[lttng-dev] Limitations on subbuf_size / num_subbuf?

[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 ;)


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 
>>>
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>> -- 
>> Mathieu Desnoyers
>> EfficiOS Inc.
>> http://www.efficios.com
>>
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