signifanctly slowdown of FreeBSD 8.0-CURRENT/amd64

O. Hartmann ohartman at
Mon Jun 1 08:30:23 UTC 2009

Kip Macy wrote:
>> I'm running the r193133 amd64 with a custom kernel and all debugging off
>> on an AMD Athlon64 3400+ single-core, and I haven't noticed any significant
>> slowing, although I haven't been doing any systematic benchmarking.
>> What would be the penalties of running an SMP -CURRENT kernel on
>> single-core hardware with no hyperthreading? Can anyone quantify the
>> typical added overhead?  Or, counterintuitively, would an SMP kernel
>> be better in some ways?
> He is trying to diagnose if the problem was introduced by enabling
> adaptive spinning on sx locks. They're only enabled on SMP kernels.
> Cheers,
> Kip
Well, no SMP on UP AMD CPUs without SMT means no usage of the sx locks.
As far as I know, the sx locks were introduced a couple of days ago,
weren't they?

To avoid any kind of misunderstanding, there is no permanent 'slowdown',
it occurs especially whenever the system's compiler builds world or a
kernel or heavy I/O activities occur. It seems my boxes, especially the
UP box, is freezing, no reaction on X11. Well, first time I thought it
is related to UP, low memory or especially new drm code used with X11
for acceleration, but I also realized those 'slowdown-incidents' on
boxes with multicores, 8 or more GB of RAM and no X11 installed and
running. This performance impact in  situations whenever building a
world is significant. We did not change the compiler, it is still the
old gcc 4.2, so I do not expect  an impact from new high-memory and
cpu-consuming optimization routines. I do not even benchmark my boxes
day for day, but I usually do a set of the same work on those boxes used
for scientific work, so while building world even on SMP boxes and
working after installation with the same software set reveals some
weirdness in some points.

I thought this is due some use-uninterruptable debugging switches, some
wrote the malloc code is about to change and so on so I was wondering if
there is something temporarely going on at the moment where some hints
could prevent me from building a world within this testing phase. Just


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