[lttng-dev] LTTng UST vs Syslog, Printf...

[Jim Dumont]

Hi there,

Totally true that it's a bit apples / oranges as far as comparison goes, but the comparison questions continue to come up...   so some quantitative numbers would be useful.

I would suggest something relatively simple and basic as far as performance & characteristics measurements goes - x apps, y traces / second - measure CPU, memory, i/o, file size across the various mechanisms.

The actual feature delta is very important of course - non blocking, overload protection, run-time filters, flight recorder mode, etc.   That wouldn't require a P&C comparison, some kind of a feature comparison table.

Any other suggestions would be greatly appreciated!

Regards,

/Jim

-----Original Message-----
From: Mathieu Desnoyers [mailto:mathieu.desnoyers at efficios.com] 
Sent: August-21-13 10:41
To: Jim Dumont
Cc: 'lttng-dev at lists.lttng.org'
Subject: Re: [lttng-dev] LTTng UST vs Syslog, Printf...

* Mathieu Desnoyers (mathieu.desnoyers at efficios.com) wrote:
> * Jim Dumont (jim.dumont at ericsson.com) wrote:
> > Hi there,
> > 
> > Has anyone done a recent performance and characteristics comparison between lttngust with syslog and printf?   Things like memory & cpu footprint, tps, i/o, disk space...
> 
> Not that I am aware of.
> 
> > 
> > I found this Windriver comparison from 2011:
> > https://www.google.ca/url?sa=t&rct=j&q=&esrc=s&frm=1&source=web&cd=1
> > &cad=rja&ved=0CCoQFjAA&url=https%3A%2F%2Fevents.linuxfoundation.org%
> > 2Fslides%2F2011%2Flinuxcon%2Flcna2011_wessel.pdf&ei=Y64TUu6qJqS62AXI
> > qYCYCg&usg=AFQjCNF0Q05MytPYVNWBPnUjB9LEGJfQZA
> 
> This presentation uses UST 0.x. This is _old_: it predates LTTng 2.0.
> 
> > 
> > And if I recall correctly, LTTng UST team also did a printf 
> > comparison a while back, but was wondering if someone has done more 
> > recent prototyping?  Any comparisons with syslog?
> 
> Not at this point. It would be interesting to compare:
> 
> - lttng-ust, both in "discard" and "snapshot" modes, vs
> - printf with timestamp,
> vs
> - syslog
> 
> Especially on multi-core systems, with applications generating a _lot_ 
> of log/trace data.

Just to add to the reflexion, there are key differences between lttng-ust and printf/syslog that makes comparison a bit difficult:

lttng-ust never blocks the application when buffers are full. It either discards events or overwrites the oldest information (flight recorder tracing).

printf and syslog will block the application if the disk I/O is not fast enough.

How would you recommand comparing these ?

Moreover, in order to ensure we can compare those, the printf benchmark would need to grab a time-stamp, and would need to be performed with one call per event (no more), since it is only "atomic" from the point of view of its buffer on a per-call basis. Moreover, printf is not async-signal-safe (as per signal(7)), so it should be noted that it cannot be used from a signal handler (whereas lttng-ust can be used from signal handlers).

Thanks,

Mathieu


> 
> Thanks,
> 
> Mathieu
> 
> > 
> > Regards,
> > 
> > /Jim Dumont
> > 
> > 
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> > 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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> lttng-dev at lists.lttng.org
> http://lists.lttng.org/cgi-bin/mailman/listinfo/lttng-dev

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