Dirk
Let's suppose for the moment that all prims, textures, and assets in
general were preloaded as they are for most multi-player games.
If you wanted to go to my island, you would need my island's OAR, or the
equivalent. Would the same performance issues exist in terms of having,
say 60 avatars in a region?
-paul
Dirk Husemann wrote:
> those of you that are following the SVN commit mails on opensim-dev
> will have noticed that i just checked in a bunch of patches.
>
> we recently did stress tests using (a) a bunch of modified pCampBot
> (modified so that they'd request every texture in sight), (b) a group
> of volunteers (30-40 clients), (c) an even greedier version of (a).
>
> stress test (a) looked fairly good
> (http://xyzzyxyzzy.net/2009/06/09/81/), so we optimistically scheduled
> (b).
>
> stress test (b) was a big disappointment
> (http://xyzzyxyzzy.net/2009/06/19/21/), so we went back to the drawing
> board and worked on the bots to become more like real avatars and also
> started looking at how we handle the traffic with the client.
>
> the reworked bots allowed us to recreate the scenario where we'd
> essentially render the system unusable once we got past the 20 avatar
> limit.
>
> we've concentrated on the following areas (so far):
>
> 1. texture sending
> 2. LLPacketHandler/LLUDPServer
> 3. XEngine
>
> that last one, XEngine, was an easy fix: the advertised behaviour in
> OpenSim.ini.example for idle timeout does not describe what's inside
> the can, to quote alan webb:
>
> The XEngine secition of the example ini says that the
> timeout for an iden thread is in seconds, and an example value
> of 60 is specified. In fact, this is actually resulting in a 60mS
> idle timeout, which is not normally enough for a smart thread
> to survive. I have added a multiplier to the XEngine constructor
> so that the number now matches the published behavior.
>
> texture sending was a bit more tricky, again to quote alan:
>
> This change moves texture send processing out of the main packet
> processing loop and moves it to a timer based processing cycle.
>
> Texture packets are sent to the client consistently over time. The
> timer is discontinued whenever there are no textures to transmit.
>
> The behavior of the texture sending mechanism is controlled by
> three variables in the LLCLient section of the config file:
>
> [1] TextureRequestRate (mS) determines how many times per second
> texture send processing will occur. The default is 100mS.
> [2] TextureSendLimit determines how many different textures will
> be considered on each cycle. Textures are selected by priority.
> The old mechanism specified a value of 10 for this parameter and
> this is the default
> [3] TextureDataLimit determines how many packets will be sent for
> each of the selected textures. The old mechanism specified a value
> of 5, so this is the default.
>
> So the net effect is that TextureSendLimit*TextureDataLimit
> packets will be sent every TextureRequestRate mS.
>
> Once we have gotten a reasonable feeling for how these parameters
> affect overall processing, it would be nice to automagically
> manage these values using information about the current status of
> the region and network.
>
> finally, LLPacketHandler and LLUDPServer: while looking (staring?) at
> the traces we had collected we realized that we might have an issue
> with the incoming UDP buffer --- checking the specs of both .NET and
> mono we found out that .NET uses a default socket buffer size of 8K
> and mono whatever the underlying linux OS was using, which for ubuntu
> 08.04 and SLES11 turned out to be 111K. both buffer sizes are not
> really that much (.NET's is a bit of a joke, IMHO) and checking the
> network stats we did see that the OS was dropping a considerable
> number of UDP datagrams. so, we added an option to set the receive
> socket buffer size for LLUDPServer (and also changed the max receive
> buffer size allowed by the OS via sysctl). setting it to a
> sufficiently large value got rid of the dropped UDP datagrams.
>
> looking at LLPacketHandler we realized that while we were re-using
> packets (via the packet pool) we were still doing a LOT of
> List<LLQueItem>(existing List<LLQueItem>) and object copying for stuff
> like ack sending/resending, dropping packets, etc. it turns out that
> we can in all cases accomplish the task without those List
> instantiations and copy operations.
>
> going back to our reworked, greedy bots we now got way beyond the 20
> avatar mark (repeated 30-40 greedy bots) and, though the system got
> laggy and slow, we could still move around with our observer avatars
> and use our in-world tools.
>
> so, the changes to texture sending, LLUDPServer, and the streamlining
> of all those foreach(...) loops seems to be going in the right direction.
>
> cheers,
> DrS/dirk
>
> --
> dr dirk husemann ---- virtual worlds research ---- ibm zurich research lab
> SL: dr scofield ---- drscofi...@xyzzyxyzzy.net ---- http://xyzzyxyzzy.net/
> RL: h...@zurich.ibm.com - +41 44 724 8573 - http://www.zurich.ibm.com/~hud/
>
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--
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University of Florida
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