[Opensim-dev] Packet Pooling - Should it work?

[Mike Dickson]

I'm actually not so much trying to optimize network traffic (that is
another great topic and I personally think what core should focus on is
protocols rather than code).  I'm concerned there is an issue with garbage
collection limiting scaling of the simulator.  Basically I'm of the opinion
that really the only thing that should be running in the simulator is...
the simulation.  So as much as possible pulling things out (Moving to AISv3
for inventory out of process, SSB out of process, etc would all be good
additional steps).  It's true if you're just running a standalone thats
probably overkill but I'm trying to support large regions and scale.  Hence
yes the whole stack is really the focus.

Mike

On Wed, Aug 14, 2019 at 10:54 PM Mister Blue <misterblue at misterblue.com>
wrote:

> There have been many attempts at optimizing the network traffic from the
> simulator to the clients. GP optimization confuses low level networking
> (queuing, ..) with application level (object updates before wind updates).
>
> Make sure you're thinking of the whole virtual world stack.
>
> On Wed, Aug 14, 2019 at 4:07 PM Mike Dickson <mike.dickson at utopiaskye.com>
> wrote:
>
> > So after doing some research I think my fix to this is to get as many of
> > the big allocations out of the region server as possible and secondarily
> to
> > get the rest coming from a pool where I can. I think that translates to
> the
> > follow projects:
> >
> > 1) Move GetMesh and GetTexture out of process and into a separate server
> > 2) Get the rest of the UDP allocations coming from a pool.
> >
> > For #1 there was code originally done for InWorldz/Halcyon to do that.  I
> > can try and ressurect it and interface it to the asset service (ideally
> > through the local asset cache) but I think alternatively a redo makes
> more
> > sense.
> > For #2 there is buffer pooling code in LibOMV originally in Halcyon that
> I
> > believe Cinder got upstream via Latif a while back.
> >
> > And yes I did run with -desktop mode in Mono for some time. It sort of
> > bandaids things a bit but when a GC pass does happen UDP stalls until the
> > GC completes and the protocol recovers (for reliable messages).  If you
> > extend that to a busy region with 20, 30 or more avatars it falls apart
> > quickly. Especially with everyone wearing mesh. Still probably better
> than
> > the standard GC but the real fix is to stop making garbage to collect.
> >
> > Mike
> >
> > Sent from Mail for Windows 10
> >
> > From: Leal Duarte
> > Sent: Tuesday, August 13, 2019 1:43 PM
> > To: opensim-dev at opensimulator.org
> > Subject: Re: [Opensim-dev] Packet Pooling - Should it work?
> >
> > PacketPool.cs code has been in usage, and still is in same packets, but
> of
> > limited usefulness
> > in same cases it could even be GC induced pseudo memory leak.
> >
> > It was replaced by a simpler pool of memory buffers (actually libomv
> > UDPPacketBuffers, but not its objectpool) on most sent packets and
> receive
> > buffers
> > also used as temporary work buffers on a few other places.
> > Most send packets have nothing to reuse but the buffer.
> >
> > Try running opensim in Workstation (desktop on mono) mode.
> > Server mode heuristics don't seem to match opensim needs that well.
> >
> > Ubit
> >
> > On 13-Aug-19 16:04, Mike Dickson wrote:
> > > I've been investigating UDP stalls for a while now and at least in some
> > > cases I'm fairly convinced some cases occur due to GC pauses.  There is
> > > some packet pooling code in the underlying LibOMV probably originally
> > > derived from work done on Halcyon to address this case.   I don't see
> any
> > > attempt in the UDP comms to make use of these buffer pools.
> > >
> > > There is seperate code in PacketPool.cs to,  I think reuse packet
> buffers
> > > based on a couple of buffer sizes and it looks like this should be on
> by
> > > default but I can't find any evidence by looking at status of any
> packet
> > > reuse occuring.  That is it looks like there is code there but it's
> > either
> > > switched off somewhere else or just doesn't work (or the stats are
> wrong
> > :).
> > >
> > > Should this PacketPooling be functional?  Alternatively has any attempt
> > > been made to wire in the PacketBuffer support thats already in LibOMV?
> > >   I'm going to dig through all this as I have time but I figured a
> little
> > > information might help short circuit some paths and direct my search.
> > >
> > > Thanks!
> > >
> > > Mike
> > > _______________________________________________
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