Subj : Re: Hazard Pointers w/o memory barrier.
To   : comp.programming.threads
From : Chris Thomasson
Date : Mon May 02 2005 08:07 pm

> Finally getting around to modifying my current RCU
> implementation to see how fast this will run.  Just
> taking the memory barriers out gave a 3x improvement
> in read access throughput.  At that rate that can be
> considered as effectively zero overhead.

Yes it can. I have already been experimenting with it for a couple of days 
and am extremely pleased with the initial results. The thing that makes me a 
bit uneasy with my windows ( and some other os's ) implementation is the 
dependence on undocumented functions. All of my code that uses this form of 
garbage collection could suddenly stop working when the next service pack 
gets installed...

;)




> About a 3x
> slowdown in write access but that's because I don't
> have the SMR logic in yet plus I have to stay with a
> slightly crippled version of RCU to avoid imperial
> entanglement.

We aren't the programmers there looking for...  ;)

Seriously though, this is why I don't provide the public with my user-space 
rcu ( URCU ) implementation. Did you inform McKenney that you were posting 
your algorithm? I am not sure if I need to ask permission...




> Adding the SMR logic should give me a
> dramatic improvement in write throughput.

Yeah. Original SMR is well suited for high write throughput because of the 
guarantees it puts on the way nodes are deleted. This new URCU_SMR thing 
can't seem to handle frequent and persistent writes as good as the original. 
It caused some problems in a couple of my algorithms. Its probably a good 
idea to export two versions of SMR...

:)

.