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<div>Hi Divya,<br>
<br>
I'm putting you back on the lttng-dev mailing list, please reply
to that list in the future so other people can answer, because I
think that trace synchronization is not exactly what you are
looking for here...<br>
<br>
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<div>I tried the sessions at same time and
communication events in between and it worked :)<br>
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I am getting quality as accurate and I can see both
traces merged .<br>
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Excellent!<br>
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Now I come at my second point i.e taking traces from
lttng sessions at different machines and at different
time and may be communication events or might be not.<br>
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If the sessions are taken are different moments, they can _never_
synchronize. Trace synchronization first matches events such that
one single event from a trace (for example "sending a packet") can
be correlated to exactly one event in the second trace (the
reception of that packet). If that is the case, the first event can
have a timestamp of now and the second be timed to January 1st 1970,
trace synchronization will work and the 2 traces will have a common
time reference after synchronization.<br>
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So In my opinion I need to apply time offset on one of the
trace to match the beginning so that they can be
synchronized . <br>
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So like first trace timestamp starts at 07:13:59 .499 222
870 and other starts at 11:21:35.537 682 885 . Then I can
apply timeoffset ( How much offset ? In apply time offset
advanced option If reference time is 7:13.... then target
time will be 11:21:35... it will calculate the offset ) on
one of the trace to match traces .<br>
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Is it possible to synchronize the traces then ? Actually I
tried these steps but not getting the synchronized traces but
then both traces beginning is exactly same ( obviously it will
as applied by the offset) <br>
<br>
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Please let me know how can I synchronize the traces from
different machines and at different time <br>
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I'm not sure what your end goal is exactly. Do you want to compare
trace executions? I am cc'ing François Doray who is currently
working on a trace comparison utility. Here's a presentation he did
recently:
<a class="moz-txt-link-freetext" href="http://ahls.dorsal.polymtl.ca/system/files/Comparison%20of%20Traces%20to%20Diagnose%20Performance%20Variations.pdf">http://ahls.dorsal.polymtl.ca/system/files/Comparison%20of%20Traces%20to%20Diagnose%20Performance%20Variations.pdf</a><br>
<br>
His work is still experimental and available on github. If that's
what you're interested in, he might give you some information on how
to use it.<br>
<br>
Otherwise, please explain what you are trying to achieve.<br>
<br>
Geneviève<br>
<br>
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<div class="gmail_extra"><br>
<div class="gmail_quote">On Thu, Jan 8, 2015 at 12:39 AM,
Geneviève Bastien <span dir="ltr"><<a
moz-do-not-send="true" href="mailto:gbastien@versatic.net"
target="_blank">gbastien@versatic.net</a>></span>
wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0
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<div text="#000000" bgcolor="#FFFFFF"><span class="">
<div>On 15-01-07 11:32 AM, Divya Vyas wrote:<br>
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<blockquote type="cite">
<p dir="ltr">Hi ,</p>
<p dir="ltr">I have some comments below and thanks a
lot for your help</p>
<p dir="ltr">On Jan 7, 2015 7:55 PM, "Geneviève
Bastien" <<a moz-do-not-send="true"
href="mailto:gbastien@versatic.net"
target="_blank">gbastien@versatic.net</a>>
wrote:<br>
><br>
> Hi Divya,<br>
><br>
><br>
> On 15-01-07 01:24 AM, Divya Vyas wrote:<br>
>><br>
>><br>
>> Hi Genevieve,<br>
>><br>
>> My target to is merge the traces of two
different machines taken on different time or same
time .<br>
><br>
> Trace synchronization works by first matching
events corresponding to the sending and the
reception of a TCP packet from both traces, and then
taking those matched events and computing a formula
that will transform timestamps from one trace to the
same clock as another trace. So only traces taken at
the same time (meaning together, not the same clock
time of course) will work.<br>
</p>
<p dir="ltr">I am not getting this last point , where
the traces are taken together. You mean that we
start lttng session on two machines at around same
time and then during session use some communication
events . Then take the traces into tracecompass for
synchronization in experiment. I am not getting in
which cases time offset is needed? </p>
</blockquote>
<br>
</span> Yes, two sessions on two machines at the same time
and they communicate during those sessions. Then you can
synchronize traces. The following traces are used in unit
tests to test trace synchronization if you wish to see
what it looks like:
<a moz-do-not-send="true"
href="http://archive.eclipse.org/tracecompass/test-traces/ctf/synctraces.tar.gz"
target="_blank">http://archive.eclipse.org/tracecompass/test-traces/ctf/synctraces.tar.gz</a><span
class=""><br>
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<blockquote type="cite">
<p dir="ltr">In what traces I need to apply time
offset so that their beginning matches. Is it
applicable on the above case which I am thinking
above.<br>
</p>
</blockquote>
<br>
</span> You never _need_ to apply time offset. It is if
you have traces that do not contain communication events,
and you want one of them to be offsetted by a certain
time. For example, you have a trace taken GST-5 and one at
GST, you cannot synchronize them because they don't have
communication events but you want to analyze them with the
same time reference, you would offset the one at GST-5 by
+5 hours.<br>
<br>
Or if you have a custom event that you know happened at
the same time on both traces, but synchronization does not
support that event, then you can offset one trace so that
both events from both traces have the same timestamp.<br>
<br>
Time offsetting is a manual process by the user, while
trace synchronization is an automatic analysis using
pre-defined events to compute a formula to transform
timestamps from one trace to the same clock as the other.<span
class=""><br>
<br>
<blockquote type="cite">
<p dir="ltr"> ><br>
><br>
>><br>
>> Actually synchronization was not working on
different machine so I tried on same machine. But
now I got it correctly I think so :)<br>
><br>
> Indeed, you have the right events now, with the
net_dev_queue and netif_receive_skb. So you should
be OK. But I *think* this method works only when on
a LAN. If your computers communicate through
internet, you're better off with the
inet_sock_local_[in|out] method</p>
<p dir="ltr">They are connected through LAN only.<br>
</p>
<p dir="ltr">><br>
>><br>
>> For different time we need to apply offset
so that their beginning matches. I think I need to
do this .<br>
>><br>
>> I tried applying offset on eclipse luna ( I
added linux tools in install new software) but I
am not getting this option " Apply time offset ". <br>
><br>
> It is in master only so far, so you should use
tracecompass to have this option.<br>
><br>
>><br>
>> I tried on tracecompass also, where I am
getting time offset option but the synchronization
view is empty . The window is not showing anything.
The tracecompass version is 0.1.0<br>
><br>
> The time offset does not involve
synchronization at all, it is just an offset, so you
would not see anything in the synchronization view.
But in the "Properties" view, when you select the
trace, the time offset is displayed.</p>
<p dir="ltr">I meant to say that I tried synchronizing
the traces in tracecompass without time offset . The
synchronizing view is empty.<br>
It should show at least quality absent etc. </p>
</blockquote>
<br>
</span> Quality absent would show only if the traces are
from different machines. If you are trying to synchronize
traces from the same machine, that view will stay empty. <br>
<span class="HOEnZb"><font color="#888888"> <br>
Geneviève<br>
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