[ros-users] rosbag playback speed

[Daniel Grollman]

Excellent, thank you so much for confirming this.  We need to stick with
Ubuntu 9.10, but we'll try upgrading to cturtle.

On 07/30/2010 07:30 PM, Jeremy Leibs wrote:
> Sorry for the typo, I meant to say that  playback on *cturtle* invoked
> the callback 2494 times.
> 
> On Fri, Jul 30, 2010 at 10:26 AM, Jeremy Leibs <leibs at willowgarage.com> wrote:
>> Daniel,
>>
>> For very high-rate things across many channels, what Blaise is talking
>> about might lead to problems.  However, I don't think it is in this
>> particular case.
>>
>> I ran your tests and checked with rxbag and the packets seem to be
>> nicely distributed as we would want.
>>
>> I am 99% confident that this is a problem with rosbag in boxturtle.
>> The old rosbag (which actually called through to rosplay), had a lot
>> of problems in the timing engine that led to this kind of bursty
>> behavior on playback.  For cturtle, I rewrote the rosbag timing engine
>> and I believe it is now far more robust and well-behaved.
>>
>> I just confirmed playback from boxturtle only invoked the callback 54
>> times.  Playback on boxturtle invoked the callback 2494 times.
>>
>> If you can possibly move to cturtle, I believe that should solve your
>> issues.  If you really need to work with boxturtle I can investigate
>> the possibility of patching in some of these timing fixes.
>>
>> --Jeremy
>>
>> On Fri, Jul 30, 2010 at 10:03 AM, Daniel Grollman
>> <daniel.grollman at epfl.ch> wrote:
>>> Hi Blaise,
>>>
>>>        Thanks for this info, I hadn't thought to consider the scheduler.
>>> However, opening up my bagfile with rxbag (and zooming in very close),
>>> it looks like there is indeed a packet every 2ms.  I'll try to confirm
>>> this with the API.
>>>
>>> Dan
>>>
>>> On 07/30/2010 06:15 PM, Blaise Gassend wrote:
>>>> As far as I know, rosbag can only rely on message arrival times when it
>>>> records a data stream. At 500 Hz, your messages are being sent at a rate
>>>> that is fast compared with Linux's scheduling granularity, so on a
>>>> loaded system, I would not expect rosbag to necessarily be scheduled
>>>> each time it receives a message. Hence it will receive the messages in
>>>> clumps, and during replay, messages will be played back in clumps. You
>>>> can verify whether this is the case by looking at the timestamps in the
>>>> bag. I think rxbag should allow you to view the timestamps graphically.
>>>> The python bag API should allow you to view the timestamps directly.
>>>>
>>>> You might be able to improve things by puting rosbag on one of the
>>>> "realtime" queues using schedtool.
>>>>
>>>> You can also see the scheduling happening using the kernel ftrace
>>>> mechanism.
>>>>
>>>> On Fri, 2010-07-30 at 14:02 +0200, Daniel Grollman wrote:
>>>>> Hello,
>>>>>
>>>>>      I've noticed some odd behavior with rosbag.  I'm generating data at
>>>>> 500hz, and recording a bag.  However, when playing back the bag, only a
>>>>> fraction of the messages reach my callback.  I believe that rosbag is
>>>>> 'bursting' the messages, i.e., sporadically sending them at much faster
>>>>> than 500 Hz, so they are then getting lost as my queue size is only 1
>>>>> (which is what I want).
>>>>>
>>>>> I'm running ros 1.0.4, and ubuntu 9.10.  I've put together a little demo
>>>>> of this issue, code is here:
>>>>>
>>>>> http://lasa.epfl.ch/~dang/rosbag_test.tar.gz
>>>>>
>>>>> Thank you,
>>>>>
>>>>> Dan Grollman
>>>>> EPFL
>>>>> _______________________________________________
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>>>>> ros-users at code.ros.org
>>>>> https://code.ros.org/mailman/listinfo/ros-users
>>>>
>>>>
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>>
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