User:Babbage Linden/Office Hours/2009 02 04

Transcript of Babbage Linden's office hours:

[8:03]	WolfPup Lowenhar:	morning babbage
[8:03]	Arawn Spitteler:	It's rather quiet; is Babbage not here? Just arrivee?
[8:03]	Nock Forager:	Hi Babbage
[8:03]	Babbage Linden:	morning all
[8:03]	Babbage Linden:	(or afternoon)
[8:03]	Imaze Rhiano:	good day
[8:03]	Fake Fitzgerald:	hi Babbage!
[8:03]	Babbage Linden:	let me ping the groups
[8:03]	Fake Fitzgerald:	midnight here :)
[8:04]	Imaze Rhiano is cooking some food for family. same time....
[8:04]	Arawn Spitteler imagines a fake oasis: Midnight at the Oa-sis... Send your camel to beh-hed...
[8:05]	Babbage Linden:	let's give people a couple of minutes to arrive
[8:06]	Alexcalle Skall:	Hello
[8:06]	WolfPup Lowenhar:	hope your office hour dose not get hit with a restart like CG's did yesterday
[8:07]	Babbage Linden:	ok, so, we've been doing quite a lot of work on mono this week
[8:07]	Babbage Linden:	looking in to the scheduler problems with 1.25
[8:07]	Babbage Linden:	there were 2 related problems
[8:08]	Babbage Linden:	first, it was possible in some circumstances for scripts to cause high time dilation, due to not yielding correctly
[8:08]	Babbage Linden:	second, we found that the memory accounting was coupled to the scheduler, so when we changed the scheduler to fix the first problem, some scripts started having stack/heap collisions
[8:08]	Babbage Linden:	i've just submitted a QAR for a new branch that should fix both problems
[8:09]	Babbage Linden:	it decouples scheduling and memory accounting
[8:09]	Babbage Linden:	and fixes the scheduler to make scripts yield correctly
[8:09]	Babbage Linden:	because both changes can have adverse effects on scripts, we're planning to release these changes as a beta server
[8:10]	Babbage Linden:	and allow you to test your scripts on aditi before we deploy the changes on the main grid
[8:10]	Babbage Linden:	in particular, if your script comes close to exhausting memory, you should test it in the beta
[8:10]	Alexcalle Skall:	but it is like an opensim? Or will be a client version?
[8:10]	Babbage Linden:	as it may have been getting away with briefly using more memory than it was entitled to
[8:11]	Babbage Linden:	and if your script is heavily reliant on slow script calls
[8:11]	Babbage Linden:	like list manipulation or sorting
[8:11]	Myla Moody:	this is for mono compiled scripts only, or lso as well?
[8:11]	Babbage Linden:	you should test your scripts on the beta
[8:11]	Babbage Linden:	the changes only affect mono scripts
[8:11]	Babbage Linden:	and will only affect a small percentage of scripts
[8:11]	Myla Moody:	thank you
[8:12]	Babbage Linden:	we'd like to get a feel for how many scripts this affects
[8:12]	Babbage Linden:	so, if you test scripts that use a lot of memory or slow functions and they work fine
[8:12]	Babbage Linden:	let us know, as well as if you have problems
[8:12]	Babbage Linden:	periapse will be organising the beta and communication
[8:13]	Babbage Linden:	so, he'll be working out how to collect and analyse feedback
[8:13]	Babbage Linden:	the changes still need to go through the QAR process
[8:14]	Babbage Linden:	but if that goes well, some regions with the changes should be available on the beta grid in a couple of weeks
[8:14]	Babbage Linden:	in the meantime we've reverted the scheduler changes we made in 1.25.4, so scripts should be running as normal on 1.25.5
[8:15]	Babbage Linden:	have any of you had any problems with memory or performance of mono scripts in 1.25.4?
[8:15]	WolfPup Lowenhar:	i have not
[8:15]	Cale Flanagan:	my greeter script greeted ne with stack overflow, so yes:)
[8:16]	WolfPup Lowenhar:	and i have some vendor the use database and emailing scripts out wuith not problems in them that i can tell
[8:16]	Alexcalle Skall:	Normally I use mono but my scripts are very light memory.
[8:16]	Babbage Linden:	so, those problems should be resolved in 1.25.5
[8:16]	Alexcalle Skall:	So i can't test it
[8:16]	Cale Flanagan:	would be an idea if list fuction could work on sourcelist and dont need a temporary list to hold data i throw away
[8:16]	Babbage Linden:	and i encourage you to test them in the beta once it's availabe
[8:17]	Babbage Linden:	there are lots of improvements we could make to the list processing functions
[8:17]	WolfPup Lowenhar:	alexcalle you can see an improvement in generaly script performance if your convert them to mono
[8:17]	Alexcalle Skall:	Yuuuuuuuus!
[8:17]	Babbage Linden:	one big reason that they're slow is that we need to convert them from mono arrays to LSL lists when we pass them to library functions
[8:18]	Babbage Linden:	but, as many of the functions don't need access to the sim internals, we could instead operate on the mono arrays directly
[8:18]	Babbage Linden:	this would be a particularly big win for functions that are used to treat lists as arrays anyway
[8:19]	Babbage Linden:	the reason we haven't done that so far is that we'd end up with 2 implementations of the library functions to maintain
[8:19]	Cale Flanagan:	would be great:) otherwise i would ask for writing my own memorycode in c:)
[8:19]	Babbage Linden:	the LSL implementation
[8:19]	WolfPup Lowenhar:	that would be nice if could get mult dementional ararys going in mono
[8:19]	Babbage Linden:	and the mono implementation
[8:19]	Babbage Linden:	so, if we can get away with using a single implementation we will
[8:20]	Cale Flanagan:	convert them for lso use...
[8:20]	Babbage Linden:	even with the copying between mono and C++ the list functions are still faster than when called from LSO
[8:21]	Babbage Linden:	the reason that list manipulation ends up using a lot of memory is that LSL has value semantics
[8:22]	Babbage Linden:	so, when you execute an expression like l = somefunc(l) there are 2 copies of l in existence until the final assignment
[8:22]	Babbage Linden:	it was in these kind of instances that mono allowed scripts to briefly use too much memory
[8:23]	Babbage Linden:	so if you use those kind of expressions in your scripts you should definitely test them in the upcoming beta
[8:24]	Babbage Linden:	also, you should avoid using the l = (l=[]) + l + new_item syntax when using mono
[8:24]	WolfPup Lowenhar:	ok will havce to take one of my fossl vendors to the beta then
[8:24]	Arawn Spitteler doesn't see why there'd be two values of l, if l is simply the final storage bucket, for the new value. it would be the assignment operator and the somefunc that would be using memory.
[8:24]	Babbage Linden:	although it's more memory efficient with LSL, it's worse with mono
[8:25]	Hidenori Glushenko:	worse?
[8:26]	Babbage Linden:	the list assignments allocate new lists
[8:26]	Babbage Linden:	so l = (l=[]) + l + item
[8:26]	Babbage Linden:	creates a new mono array for []
[8:26]	Babbage Linden:	which allocates some memory
[8:27]	Babbage Linden:	if you just did l += item
[8:27]	Babbage Linden:	the allocation would be avoided
[8:27]	Babbage Linden:	once the final assignment has finished, then the memory will be reclaimed
[8:27]	Babbage Linden:	but the extra complicated expression requires more memory while executing
[8:28]	Hidenori Glushenko:	I understand, thanks babbage.
[8:28]	Babbage Linden:	the way memory accounting works with mono is that we measure the size of the script when it's not running
[8:28]	Babbage Linden:	and add the size of the bytecode
[8:28]	Babbage Linden:	the minimum size of a mono script is 4K
[8:28]	Babbage Linden:	so, when you start running, you have 60K available
[8:29]	Arawn Spitteler:	"Start Running," means an event is called?
[8:29]	Babbage Linden:	during your time slice you might allocate 2K of memory, but end up only referencing 1K at the end of your time slice
[8:30]	Babbage Linden:	so, at the end of the time slice, the memory accounter will determine you have 59KB available
[8:30]	Babbage Linden:	but while you're running the sim thinks you might only have 58K free
[8:30]	Babbage Linden:	as you get close to using up all your memory, this difference matters
[8:31]	Babbage Linden:	it can mean the difference between a running script and a stack heap collision
[8:31]	Babbage Linden:	so, when writing scripts in mono, you should avoid creating temporary variables if you can
[8:33]	Babbage Linden:	does that make sense?
[8:33]	WolfPup Lowenhar:	i know i try to have all myne global to start with
[8:33]	Babbage Linden:	good
[8:34]	Babbage Linden:	actually, it's only lists and strings you need to be careful about as they use heap memory
[8:34]	Babbage Linden:	all other types use stack memory
[8:34]	Arawn Spitteler was doing some thing convoluted, the other day: something = llList2Rot(llGetObjectDetails(llGetLinkKey(2), [OBJECT_ROT]),0 or something like that. Should that be broken, or compiled with other expressions?
[8:35]	Babbage Linden:	so, using local rotations, vectors and integers won't impact memory usage
[8:35]	WolfPup Lowenhar:	sometimes it can be dificult though when your having to convert one that was orginaly written in LSL to mono though when you did not make the orginal
[8:35]	Babbage Linden:	but lists, strings and keys (which are implemented as strings) should be avoided where possible
[8:35]	Babbage Linden:	WolfPup, yes
[8:36]	Babbage Linden:	but all LSL scripts should have enough memory when converted to mono
[8:36]	Babbage Linden:	(the opposite isn't true)
[8:36]	Babbage Linden:	if you start changing a script that used to be LSL and start running out of memory
[8:37]	Babbage Linden:	look for temporary lists, strings and keys that you can remove
[8:37]	Babbage Linden:	especially the l = (l=[]) + l + item construction
[8:37]	Babbage Linden:	ok, unfortunately i've got to run off to help another linden
[8:37]	WolfPup Lowenhar:	would it be better to make them global(putting them at the start of the script)
[8:37]	Babbage Linden:	so i'm going to have to cut our meeting short today
[8:38]	Babbage Linden:	but i hope that's been useful
[8:38]	Cale Flanagan:	without + item is was very usefull to get again old memory usage...
[8:38]	Babbage Linden:	and that you'll be able to test your scripts on the beta grid soon
[8:38]	Babbage Linden:	thanks for coming everyone
[8:38]	Mystical Cookie:	thank you for your time :)
[8:38]	Babbage Linden:	hope to see you next time
[8:38]	WolfPup Lowenhar:	Thank Youuuuuu!! for the tip for having us here babbage
[8:38]	Fake Fitzgerald:	thanks Babbage
[8:38]	Nock Forager:	thanks babbage.
[8:39]	WolfPup Lowenhar:	dang hosting gesture :)
[8:39]	Babbage Linden:	bye!
[8:39]	WolfPup Lowenhar:	babbag i have one question can an email script in the beta grid comunicate with a 'server' on the main grid?
[8:40]	Arawn Spitteler:	We shold be ble to; shouldn't we?
[8:40]	Myla Moody:	i would be surprised if the uuid mappings cross grids, but would be fun to test :)