2010-05-14 Rodrigo Kumpera <rkumpera@novell.com>

2010-05-14 Rodrigo Kumpera  <rkumpera@novell.com>

	* sgen-gc.c (global_remset_cache_test): New function that
	implements a 2 element LRU cache for just added remsets.
	It is used to avoid adding duplicate ones.

	* sgen-gc.c (add_to_global_remset): Check cache	before
	adding new entry.

	* sgen-gc.c (scan_from_remsets): Ditto.

	A 2 element LRU cache was chosen by profiling IronPython 2.6
	pytones with 1M passes and corlib compilation.

	For the ipy test duplication was originally 940.92, measured
	by "Store remsets" divided by "Unique store remsets".

	With a 2-element LRU, duplication went to 1.007. Without the
	check in scan_from_remsets 1.438.

	With a 16-elements LRU, duplication reduction was negligibe.
	A single element cache was basically of no use.

	With corlib compilation duplication went from  1.4 to 1.02.

	Performance results is a 20% time decrease for ipy and 2%
	with corlib.

git-svn-id: svn+ssh://mono-cvs.ximian.com/source/trunk/mono@157460 e3ebcda4-bce8-0310-ba0a-eca2169e7518