[Pharo-project] Method cache
Hi! I think I already know the answer, but I would like to ask still. Is there a way in Pharo to know about cache misses? Is there a way to know about the method cache within the image? I guess no. Would it be hard to add this information? Cheers, Alexandre -- _,.;:~^~:;._,.;:~^~:;._,.;:~^~:;._,.;:~^~:;._,.;: Alexandre Bergel http://www.bergel.eu ^~:;._,.;:~^~:;._,.;:~^~:;._,.;:~^~:;._,.;:~^~:;.
2010/1/8 Alexandre Bergel <alexandre@bergel.eu>:
Hi!
I think I already know the answer, but I would like to ask still. Is there a way in Pharo to know about cache misses? Is there a way to know about the method cache within the image? I guess no. Would it be hard to add this information?
This is a 'magic' which sits deeply in VM. Image-side stuff should not care about it much, since it is implementation specific. Mainly, because VM could employ different cache strategies , and by not exposing it, we making sure that we could change it at any moment. Especially , if we think about JIT and method inlining...
Cheers, Alexandre -- _,.;:~^~:;._,.;:~^~:;._,.;:~^~:;._,.;:~^~:;._,.;: Alexandre Bergel  http://www.bergel.eu ^~:;._,.;:~^~:;._,.;:~^~:;._,.;:~^~:;._,.;:~^~:;.
_______________________________________________ Pharo-project mailing list Pharo-project@lists.gforge.inria.fr http://lists.gforge.inria.fr/cgi-bin/mailman/listinfo/pharo-project
-- Best regards, Igor Stasenko AKA sig.
This is what I expected. Thanks Igor, Alexandre On 8 Jan 2010, at 11:23, Igor Stasenko wrote:
2010/1/8 Alexandre Bergel <alexandre@bergel.eu>:
Hi!
I think I already know the answer, but I would like to ask still. Is there a way in Pharo to know about cache misses? Is there a way to know about the method cache within the image? I guess no. Would it be hard to add this information?
This is a 'magic' which sits deeply in VM. Image-side stuff should not care about it much, since it is implementation specific. Mainly, because VM could employ different cache strategies , and by not exposing it, we making sure that we could change it at any moment. Especially , if we think about JIT and method inlining...
Cheers, Alexandre -- _,.;:~^~:;._,.;:~^~:;._,.;:~^~:;._,.;:~^~:;._,.;: Alexandre Bergel http://www.bergel.eu ^~:;._,.;:~^~:;._,.;:~^~:;._,.;:~^~:;._,.;:~^~:;.
_______________________________________________ Pharo-project mailing list Pharo-project@lists.gforge.inria.fr http://lists.gforge.inria.fr/cgi-bin/mailman/listinfo/pharo-project
-- Best regards, Igor Stasenko AKA sig.
_______________________________________________ Pharo-project mailing list Pharo-project@lists.gforge.inria.fr http://lists.gforge.inria.fr/cgi-bin/mailman/listinfo/pharo-project
-- _,.;:~^~:;._,.;:~^~:;._,.;:~^~:;._,.;:~^~:;._,.;: Alexandre Bergel http://www.bergel.eu ^~:;._,.;:~^~:;._,.;:~^~:;._,.;:~^~:;._,.;:~^~:;.
Many many years ago I looked at method caching and how it relates to findings in the "Green Book" and testing showed the same assumptions and results, "a 96.4% cache hit ratio." Here's a note from 2001.
Well back on march 8th 2001 I looked into this (at least the cache part). So I'll quote a part from my discussion with Dan:
"Now in mapPointersInObjectsFromto we call mapInterpreterOops which calls flushMethodCache.
Now I was thinking. Watching snow fall is boring after awhile, that couldn't we be smart and delete entries in the cache by looking at it and the range of memory? The trade is how expensive to check and of course being sure it's correct.
So I moved flushMethodCache into mapPointersInObjectsFromto from it's location in mapInterpreterOops and created a new routine like below which considers if the cache values of oops map to a location within the range of interest, then I clear the cache value.
I ran this for a little while and found I had
1356 flush calls which only resulted in 856 cache entries being invalidated. This seems much better than flushing all 512 entries in the method cache on each incremental GC event. I also noted that in lookupInMethodCacheSelclass, the number of calls was about 50 million,and cache hits: 20M on probe1, 16M on probe2, 11M on probe3 and 1.8M not found
BTW I looked at atCache, but mmm 'since objects die young' found that over 70% of the at cache would be flushed at any given incremental GC event. (IE 70% of the time objects were in new space)." ----------------
The change made way back then was to flush the cache by location because most flush are a result are newspace GC invocations, and the number of methods in NewSpace is very low. You will note the fact that the method cache of 512 had a 96.4% cache hit ratio.
Since you can run the Squeak VM in Squeak I'd think you could easily build an instrumented VM that collects bytecode statistics to compare to number in the green book.
Also note that Scott A Crosby <crosby@qwes.math.cmu.edu> on Sun Dec 9, 2001wrote "New method cache, 30% faster macrobenchmarks and ineffeciencies."
One should look in the archives for the details
Mmm now if I recall I'm sure Tim, Ian and I looked (yes in sept 2002) into just the caching changes and couldn't generate the numbers that justified the complexity (or the extra memory) for the change required.
On Tuesday, May 13, 2003, at 07:01 AM, Alexandre Bergel wrote:
Hello!
By reading the green book, I have some question related the send bytecode (page 210): - "Approximately every third instruction is a message send and sends requiring dictionary lookups occur every 6.667 bytecodes. Of the sends needing dictionary searches, 36.64% invoked primitives, and the rest resulted in the execution of a Smalltalk method which, along with process switches, accounted for a context switch every 6.50 > bytecodes." - "... 78.92% are arithmetic and logical operations..."
This article was made in 1982, I would like to know it these proportion are still equivalent nowadays.
A bit related to this, what is the effect of the method cache? In the average, what is the % of the method found in the cache?
I heard once that only 1/10th of the message send are really polymorphic, and the rest is mono-morphic.
Cheers, Alexandre
-- _,.;:~^~:;._,.;:~^~:;._,.;:~^~:;._,.;:~^~:;._,.;: Alexandre Bergel http://www.iam.unibe.ch/~bergel ^~:;._,.;:~^~:;._,.;:~^~:;._,.;:~^~:;._,.;:~^~:;.
--
On 2010-01-08, at 6:23 AM, Igor Stasenko wrote:
2010/1/8 Alexandre Bergel <alexandre@bergel.eu>:
Hi!
I think I already know the answer, but I would like to ask still. Is there a way in Pharo to know about cache misses? Is there a way to know about the method cache within the image? I guess no. Would it be hard to add this information?
This is a 'magic' which sits deeply in VM. Image-side stuff should not care about it much, since it is implementation specific. Mainly, because VM could employ different cache strategies , and by not exposing it, we making sure that we could change it at any moment. Especially , if we think about JIT and method inlining...
Cheers, Alexandre -- _,.;:~^~:;._,.;:~^~:;._,.;:~^~:;._,.;:~^~:;._,.;: Alexandre Bergel http://www.bergel.eu ^~:;._,.;:~^~:;._,.;:~^~:;._,.;:~^~:;._,.;:~^~:;.
-- =========================================================================== John M. McIntosh <johnmci@smalltalkconsulting.com> Twitter: squeaker68882 Corporate Smalltalk Consulting Ltd. http://www.smalltalkconsulting.com ===========================================================================
participants (3)
-
Alexandre Bergel -
Igor Stasenko -
John M McIntosh