[lttng-dev] Limitations on subbuf_size / num_subbuf?

[Mathieu Desnoyers]

* 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.

Messing with defaults in packaging seems odd.

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