Date: Wed, 30 Aug 2006 11:12:39 -0700 (PDT) From: backyard <backyard1454-bsd@yahoo.com> To: Jordi Carrillo <jordilin@gmail.com>, freebsd-questions@freebsd.org Subject: Re: SMP detection Message-ID: <20060830181240.65785.qmail@web83106.mail.mud.yahoo.com> In-Reply-To: <94ff3700608301020l34251166nbdb4d72842e1bb86@mail.gmail.com>
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--- Jordi Carrillo <jordilin@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@freebsd.org mailing list > http://lists.freebsd.org/mailman/listinfo/freebsd-questions > To unsubscribe, send any mail to > "freebsd-questions-unsubscribe@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
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