Nadia.Derbey@bull.net wrote:
> After scalability problems have been detected when using the sysV ipcs, I
> have proposed to use an RCU based implementation of the IDR api instead (see
> threads http://lkml.org/lkml/2008/4/11/212 and
> http://lkml.org/lkml/2008/4/29/295).
> 
> This resulted in many people asking to convert the idr API and make it
> rcu safe (because most of the code was duplicated and thus unmaintanable
> and unreviewable).
> 
> So here is a first attempt.
> 
> The important change wrt to the idr API itself is during idr removes:
> idr layers are freed after a grace period, instead of being moved to the
> free list.
> 
> The important change wrt to ipcs, is that idr_find() can now be called
> locklessly inside a rcu read critical section.
> 
> Here are the results I've got for the pmsg test sent by Manfred: 
> 
>    2.6.25-rc3-mm1   2.6.25-rc3-mm1+   2.6.25-mm1   Patched 2.6.25-mm1
> 1         1168441           1064021       876000               947488
> 2         1094264            921059      1549592              1730685
> 3         2082520           1738165      1694370              2324880
> 4         2079929           1695521       404553              2400408
> 5         2898758            406566       391283              3246580
> 6         2921417            261275       263249              3752148
> 7         3308761            126056       191742              4243142
> 8         3329456            100129       141722              4275780
> 
> 1st column: stock 2.6.25-rc3-mm1
> 2nd column: 2.6.25-rc3-mm1 + ipc patches (store ipcs into idrs)
> 3nd column: stock 2.6.25-mm1
> 4th column: 2.6.25-mm1 + this pacth series.
> 


You'll find in attachment the corresponding chart, and also the pmsg 
code (originally sent by Manfred).

Regards,
Nadia