Re: 8-CPU (SMP) #s for lockfree rtcache

Dipankar Sarma
2002-05-28T16:22:34Z

Hi Robert,

On Tue, May 28, 2002 at 08:49:58AM -0700, Robert Love wrote:
>
> > Well, the last time RCU was discussed, Linus said that he would
> > like to see someplace where RCU clearly helps.
>
> I agree the numbers posted are nice, but I remain skeptical like Linus.
> Sure, the locking overhead is nearly gone in the profiled function where
> RCU is used. But the overhead has just been _moved_ to wherever the RCU
> work is now done. Any benchmark needs to include the damage done there,
> too.

Have you looked at the rt_rcu patch ? Where do you think there
is overhead compared to what route cache alread does ? In my
profiles, rcu routines and kernel mechanisms that it uses
don't show high up. If you have any suggestions, then I can
do an investigation.

>
> I also balk at implicit locking...
>

I agree that it is better to keep things simple and RCU isn't a
replacement for locking. However the route cache hash table with
refcount is a relatively simpler use of RCU and since it has
benefits, we shouldn't shy away from using it if it is useful.

Thanks
--
Dipankar Sarma <dipankar@in.ibm.com> http://lse.sourceforge.net
Linux Technology Center, IBM Software Lab, Bangalore, India.