Re: [Squeak-VMdev] Re: GC improvements

[John M M. <jo...@sm...>]

On Jan 19, 2005, at 2:38 PM, Andreas Raab wrote:

> John,
>> Jerry has to confirm what he did and if it was repeated mostly the
>> same, but it did do 65,000 to 70,000 young space GC and it appears
>> we reduced the young space GC time by 40 seconds.  This does result in
>> more full GC work (5) since I tenure about 16MB before doing a Full  
>> GC,
>> but that accounts only for an extra second of real time...
>
> Agressive tenuring would probably work around some of the problems  
> we've seen in the past (see  
> http://croqueteer.blogspot.com/2005/01/need-for-speed.html) though in  
> general, it seems as if Croquet performs significantly better if you  
> allow for more allocationsBetweenGCs - it seems as if the working set  
> of Croquet is larger than your average Squeak working set. This also  
> explains the stats you are getting - you're tenuring like mad because  
> youngSpace is too small and then at some point where you hit fullGC  
> you are "back to normal". This probably shouldn't be "fixed" by  
> tenuring but rather by tweaking the allocationsBetweenGCs.

The problem with making allocationsBetweenGCs is the average objects  
explored goes up since the number of objects that might live is   
allocationsBetweenGCs. This increases the incremental GC time by  
milliseconds which impacts timing for Delays.

>
> Also notice that the stats look like with the agressive growths logic  
> we are doing more fullGCs than without them (this isn't totally clear  
> from looking at the pictures but I would expect more spikes in the  
> before part if it had more fullGCs). This is not necessarily a good  
> thing - I would rather spend a few percent more on IGC than having to  
> run fullGCs in Croquet.

In this example the historical implementation took 57 seconds to build  
a teapot, after the change it takes 49 seconds, even if it took a  
second or two to manage the full GCs.  I'm grabbed back 8 seconds that  
is a good thing.

>
> Cheers,
>  - Andreas
>
>
--
======================================================================== 
===
John M. McIntosh <jo...@sm...> 1-800-477-2659
Corporate Smalltalk Consulting Ltd.  http://www.smalltalkconsulting.com
======================================================================== 
===