Why is MySQL nearly twice as fast on Linux/AMD64 Vs. FreeBSD/ AMD64?

[Till Plewe]

On Thu, May 20, 2004 at 05:38:31PM -0400, Haapanen, Tom wrote:
> John-Mark Gurney [mailto:gurney_j at efn.org]:
> > Well, there is two parts to SMP, one is the OS seeing the CPU, which is 
> > probably happening, since you don't see the idle time drop below 50%...  
> > to check how many cpu's FreeBSd sees, run:
> > sysctl hw.ncpu
> > I get:
> > -bash-2.05b$ sysctl hw.ncpu
> > hw.ncpu: 2
> > On a dual proc box..
> > 
> > The next part is if the program makes use of either multiple processes, 
> > or a threading library like libpthread that will support concurent threads
> > of execution...   This last part is the problem you are having...  There
> > seems to be a problem with libpthread not starting another kse (iirc) to 
> > support the extra cpu...
> 
> Right.  Looking at my production server (dual Opteron 242) it looks like I
> have essentially been running MySQL on a single CPU, too, based on the ps
> output:
> 
> root     11     0     0    0 RL    ??  61050:34.15  (idle: cpu1)
> root     12     0     0    0 RL    ??  65468:56.13  (idle: cpu0)
> 
> The idle time in the ps output should conclusively prove to JG, too, whether
> both CPUs are actually being utilized.
> 
> It sure doesn't look like the CPU time is evenly distributed across the two
> processors -- it looks like MySQL is running on CPU1 only.
> 
> I'm happy to provide access to the box if that will help someone figure out
> what's going on with the threading.
> 
> Tom

Are you running SCHED_ULE? I had a similar problem which vanished when I switched
back to SCHED_4BSD. 

- Till