Minutes from Feb 22 LSE Con Call


I. Hanna Linder - Fastwalk Patch overview and results.

	Hanna published lockstat results on http://lse.sf.net/locking
	comparing a clean 2.4.17 system with a 2.4.17 system running
	only her most recent 2.4.17 fastwalk patch. 

	Lockstat results are very promising with an almost 50% decrease in
	Big Kernel Lock (kernel_flag) and lru_list_lock contention 
	combined with almost 30% increase in dbench throughput. There is
	an infitnite loop she discvoered in testing she is tracking down.

	The idea for the fastwalk patch came from Alexander Viro
	(viro@math.psu.edu). His idea was to decrease cacheline bouncing
	based on the constant increment and decrement of a reference
	counter for each dentry in a path. Which is most strongly felt
	in paths around / since they are most commonly accessed.

	Basically in before path walking starts the dcache_lock is held 
	instead of incrementing the reference counter. Then walk the path 
	in a loop while holding the lock where that is easily done. Whenever a 
	dentry needs to be created from the fs or deleted from the dcache then 
	the dcache_lock is dropped and d_count is set back to normal to 
	proceed unchanged.

	She has cleanly applied her patch to 2.5.5 and should have results
	for that version available early next week. She is also going to
	run with lazy_lru to measure performance gains.

	Dcache ToDo: 
		Hanna send out most recent 2.4.17 patch
		Run fastwalk with lazy-lru
		Publish 2.4.17 results on lkml
		Run dbench without lockstat installed
		Send out patch for 2.5.5
		Publish results for 2.5.5 
		Look at eviction policy for future work
		Dave Olien will look at Hash functions
		Martin Bligh will let us know results on Specweb99

II. Martin Bligh - Has anyone else tried shifting page offset to something
	other than 3Gb on a large machine? We tried it and havent gotten it 
	to work very well with greater than 4G of memory. No one responded.


III. Gerrit Huizenga - For the next call Gerrit would like to see updates
	on performance related benchmarks. Particularly TPC-H, Volanomark,
	and SpecWeb99 benchmarks and anything else people have been
	running.

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minutes compiled by Hanna Linder with help from Paul Dorwin.