Date: Wed, 30 Aug 2006 23:37:02 +0200 From: "Jordi Carrillo" <jordilin@gmail.com> To: skylar@cs.earlham.edu Cc: backyard1454-bsd@yahoo.com, freebsd-questions@freebsd.org Subject: Re: SMP detection Message-ID: <94ff3700608301437u4ea3280ama8a9cfda3edfda08@mail.gmail.com> In-Reply-To: <44F6036E.7050203@cs.earlham.edu> References: <94ff3700608301020l34251166nbdb4d72842e1bb86@mail.gmail.com> <20060830181240.65785.qmail@web83106.mail.mud.yahoo.com> <94ff3700608301302n13f9aabcs935fbe6403601d30@mail.gmail.com> <44F6036E.7050203@cs.earlham.edu>
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Skylar, So, 50% is used for processes and the other 50% to handle hardware interrupts. Is that right? 2006/8/30, Skylar Thompson <skylar@cs.earlham.edu>: > > Jordi Carrillo wrote: > > 2006/8/30, backyard <backyard1454-bsd@yahoo.com>: > >> > >> > >> > >> --- 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 > >> > > > > > > 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@cs.earlham.edu) > -- http://www.cs.earlham.edu/~skylar/ > > > > > -- http://jordilin.wordpress.com
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