Hi Divya,
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...
I tried the sessions at same time and communication events in between
and it worked :)
I am getting quality as accurate and I can see both traces merged .
Excellent!
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.
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.
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 .
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 .
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)
Please let me know how can I synchronize the traces from different
machines and at different time
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:
http://ahls.dorsal.polymtl.ca/system/files/Comparison%20of%20Traces%20to%20Diagnose%20Performance%20Variations.pdf
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.
Otherwise, please explain what you are trying to achieve.
Geneviève
On Thu, Jan 8, 2015 at 12:39 AM, Geneviève Bastien
<[email protected] <mailto:[email protected]>> wrote:
On 15-01-07 11:32 AM, Divya Vyas wrote:
Hi ,
I have some comments below and thanks a lot for your help
On Jan 7, 2015 7:55 PM, "Geneviève Bastien"
<[email protected] <mailto:[email protected]>> wrote:
>
> Hi Divya,
>
>
> On 15-01-07 01:24 AM, Divya Vyas wrote:
>>
>>
>> Hi Genevieve,
>>
>> My target to is merge the traces of two different machines
taken on different time or same time .
>
> 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.
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?
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:
http://archive.eclipse.org/tracecompass/test-traces/ctf/synctraces.tar.gz
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.
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.
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.
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.
>
>
>>
>> Actually synchronization was not working on different machine
so I tried on same machine. But now I got it correctly I think so :)
>
> 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
They are connected through LAN only.
>
>>
>> For different time we need to apply offset so that their
beginning matches. I think I need to do this .
>>
>> 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 ".
>
> It is in master only so far, so you should use tracecompass to
have this option.
>
>>
>> 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
>
> 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.
I meant to say that I tried synchronizing the traces in
tracecompass without time offset . The synchronizing view is empty.
It should show at least quality absent etc.
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.
Geneviève
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