Re: HTT on current

On Tue, 26 Aug 2003, John Baldwin wrote:

> On 26-Aug-2003 Yamada Ken Takeshi wrote:
> >   JYI,
> >   I tested machdep.hlt_logical_cpus=0/1, buildworld,
> > and found no particular reason to disable HTT
> > as below with Zeon 2.8Ghz x 2, 1GBmem, Slow IDE HDD.
> >
> >  It may not be the common case, so just for your info.
> >
> ># sysctl machdep.hlt_logical_cpus=0
> ># /usr/bin/time make -j32 buildworld
> >      1910.29 real      2520.53 user       777.30 sys
> >
> ># sysctl machdep.hlt_logical_cpus=1
> ># /usr/bin/time make -j32 buildworld
> >      2289.33 real      2666.66 user       645.88 sys
>
> One test is not sufficient.  -current is also not the best
> place to test. :)  When I first implemented HTT in -current

The above times seem slow enough to be partly the result of
debugging options in -current.  I get buildworld times ranging
from 1401 seconds (2002/09/01) to 2427 seconds (2003/05/06)
on Athlon XP1600 x 1 depending on configuration and tuning (but
never with any expensive debugging options).  A Xeon 2.8GHz x 2
should be a bit faster than an old Athlon.

> ... I did 16 trials (first one was
> throwaway) of back-to-back buildworlds of the same version
> of -stable using make, make -j2, and make -j4 for the
> following configurations: UP, HTT, HTT with smp_idle_hlt, and
> HTT with pause instructions added to stable and smp_idle_hlt.
> The fastest build time belonged to UP without any -j option.

All benchmarks using -j are invalid because of a pessimization
in make(1).  It sleeps for up to SEL_USEC = 100000 usec after
completion of every job (average 50 msec).  With -j2 this increases
!SMP buildworld times of approx. 2000 seconds by approx. 15%.  I think
it has a smaller effect for larger -j values and for SMP but haven't
benchmarked it.  This is fixed in NetBSD.  I think fixing it was more
urgent in NetBSD because NetBSD never changed SEL_USEC from its
4.4Lite default of 500000.  500000 was large enough to be noticeable
even in 1997 when it was reduced in FreeBSD.

Bruce