Re: lmbench results for 2.4 and 2.5

["Martin J. Bligh" <mbligh@aracnet.com>]

> My previous testing with unix sockets prompted me to do a few lmbench 
> runs with 2.4.19 and 2.5.65.  The results have me a bit concerned, as 
> there is no area where 2.5 is faster and several where it is 
> significantly slower.
> 
> In particular:
> 
> stat is 8 times worse
> open/close are 7 times worse
> fork is twice as expensive
> tcp latency is 5 times worse
> file deletion and mmap are both twice as expensive
> tcp bandwidth is 5 times worse
> 
> Optimizing for muliple processors and heavy loads is nice, but this 
> looks like its happening at the cost of basic performance.  Is this 
> really the route we should be taking?

I think you're jumping to conclusions about what causes this - let's
actually try to find the real root cause. These things have many different 
causes ... for instance, rmap has been found to be a problem in some 
workloads (especially things like the fork stuff). If you want to 
try 65-mjb1 with and without the the shared pagetable stuff, you
may get some different results. (if you have stability problems, try
doing a patch -p1 -R of 400-shpte, it seems a little fragile right now).

http://www.kernel.org/pub/linux/kernel/people/mbligh/2.5.65/

Also, if you can get kernel profiles for each test, that'd help to work
out the root cause.

M.