Re: ULE/SCHED_SMP diff for 7.0, buildkernel & thanks.

[Jeff Roberson <jroberson_(_at_)_chesapeake_(_dot_)_net>]

With regards to buildkernel times;  I do not want to sacrafice performance 
on other benchmarks to improve buildkernel.  The problem is that 4BSD is 
as agressive as possible at scheduling work on idle cores.  This behavior 
that helps one buildworld hurts on other, in my opinion, more important 
benchmarks.

For example: http://people.freebsd.org/~jeff/sysbench.png

ULE is 33% faster than SCHED_4BSD at this mysql test.  This is a direct 
result of prefering to idle to make more efficient scheduling decisions. 
ULE is also faster at various networking benchmarks for similar reasons.

I also believe that while the real time may be slower on buildworld the 
system and user time will be smaller by a degree greater than the delta in 
real time.  This means that while you're building packages you have a 
little more cpu time leftover to handle other tasks.  Furthermore, as the 
number of cores goes up things start to tip in favor of ULE although this 
is somewhat because it's harder for even 4BSD to keep them busy due to 
disk bandwidth.

Thanks everyone for testing.  Can someone confirm that they have tested 
with x86 rather than amd64?  I will probably commit later today.

Thanks,
Jeff

On Tue, 17 Jul 2007, Claus Guttesen wrote:

> > > sched_ule:
> > >
> > > -j 3 buildkernel: 13:23
> > > -j 4 buildkernel: 12:38
> > > -j 5 buildkernel: 12:41
> > > -j 6 buildkernel: 12:47
> > >
> > > sched_4bsd:
> > > -j 3 buildkernel: 11:43
> > > -j 4 buildkernel: 12:02
> > >
> > > So sched_ule seems to handle more processes slightly better than 4bsd
> > > albeit it does it slower. ule's sweet spot is -j 4 and 4bsd is -j 3.
> > >
> >
> > 4bsd vs ULE
> >
> > -j 3 buildkernel: 11:43 vs -j 3 buildkernel: 13:23
> >
> > -j 4 buildkernel: 12:02 vs -j 4 buildkernel: 12:38
> >
> >
> > ULE is always slower?
>
> In my case yes.
>
> --
> regards
> Claus
>
> When lenity and cruelty play for a kingdom,
> the gentlest gamester is the soonest winner.
>
> Shakespeare
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