SMP detection

[Jordi Carrillo]

Skylar,
So, 50% is used for processes and the other 50% to handle hardware
interrupts. Is that right?

2006/8/30, Skylar Thompson <skylar at cs.earlham.edu>:
>
> Jordi Carrillo wrote:
> > 2006/8/30, backyard <backyard1454-bsd at yahoo.com>:
> >>
> >>
> >>
> >> --- Jordi Carrillo <jordilin at gmail.com> wrote:
> >>
> >> > I've read that SMP should be disabled for
> >> > performance issues (I did not know
> >> > that before installing freebsd). I have a P4 3GHz
> >> > with hyperthreading
> >> > technology. I have the SMP-GENERIC kernel and it
> >> > only launches one cpu. So,
> >> > I've decided to disable SMP from BIOS. Is that ok?,
> >> > knowing that I have a
> >> > Smp enabled kernel? or should I install one without
> >> > smp? If so, is there a
> >> > way to install one already precompiled?
> >> > Thanks in advance
> >> >
> >> > --
> >> > http://jordilin.wordpress.com
> >> > _______________________________________________
> >> > freebsd-questions at freebsd.org mailing list
> >> >
> >> http://lists.freebsd.org/mailman/listinfo/freebsd-questions
> >> > To unsubscribe, send any mail to
> >> > "freebsd-questions-unsubscribe at freebsd.org"
> >> >
> >>
> >> if the system runs with one cpu now and you don't
> >> enable smp with HT with the sysctl variable then you
> >> should be ok. If your not doing SMP then recompiling
> >> the kernel for single processor mode will make things
> >> run a little quicker because the SMP code won't come
> >> into play.
> >>
> >> with HT disabling in FreeBSD is more for the security
> >> issues about a potential exploit whereby one process
> >> in one pipe can access the priveledged information of
> >> a process in another pipe because the two cores share
> >> one processor cache and thus one cache table. To my
> >> knowledge this hasn't been exploited yet.
> >>
> >> If you just install the generic kernel you it should
> >> be only the uniprocessor one. I would just do a:
> >>
> >> cd /usr/src && make buildworld && make
> >> KERNCONF=GENERIC buildkernel && make KERNCONF=GENERIC
> >> installkernel
> >>
> >> as opposed to a binary version assuming you haven't
> >> updated yet you won't have to install world but I
> >> believe it must have the build in the source tree to
> >> build a kernel. On your P4 though the difference
> >> between SMP and uniproc may not be worth the trouble
> >> because I don't think much of a gain would be made. on
> >> a P1 a much different story...
> >>
> >> if you aren't concerned with bad users or hackers
> >> hitting the box I would just enable HT with the sysctl
> >> variable. This will not make things run slower at all,
> >> just (in theory) less secure, which is why the
> >> veriable was created in the first place as I recall.
> >> If you are concerned I would wait until you update
> >> your system and then just build a GENERIC/CUSTOM
> >> kernel without the SMP option set.
> >>
> >>
> >> -brian
> >>
> >
> >
> > I will disable smp from bios. If I have a smp kernel, I suppose there
> > will
> > be no problem after all. Would that be ok?
> > The problem with having SMP enabled is that the smp kernel only
> > detects one
> > cpu and the system monitor only features one cpu as well as gkrellm (in
> > Linux it shows two cpus). When compiling the system monitor shows the
> > cpu at
> > a maximum of 50%, so what's going on with the other 50%?
> > writing machdep.hlt_logical_cpus to 2 in loader.conf does not solve
> > anything.
> I believe FreeBSD uses the other logical CPU to handle hardware
> interrupts, which can still help performance. You can check dmesg to see
> how it's actually handling it.
>
> --
> -- Skylar Thompson (skylar at cs.earlham.edu)
> -- http://www.cs.earlham.edu/~skylar/
>
>
>
>
>


-- 
http://jordilin.wordpress.com