Date: Wed, 9 Jan 2013 06:35:33 -0800 (PST) From: Barney Cordoba <barney_cordoba@yahoo.com> To: Erich Dollansky <erichsfreebsdlist@alogt.com> Cc: freebsd-net@freebsd.org, jack.vogel@gmail.com, Mark Atkinson <atkin901@gmail.com> Subject: Re: To SMP or not to SMP Message-ID: <1357742133.9692.YahooMailClassic@web121601.mail.ne1.yahoo.com> In-Reply-To: <20130109211439.5b590bf5@X220.ovitrap.com>
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--- On Wed, 1/9/13, Erich Dollansky <erichsfreebsdlist@alogt.com> wrote: > From: Erich Dollansky <erichsfreebsdlist@alogt.com> > Subject: Re: To SMP or not to SMP > To: "Barney Cordoba" <barney_cordoba@yahoo.com> > Cc: "Mark Atkinson" <atkin901@gmail.com>, freebsd-net@freebsd.org, jack.vogel@gmail.com > Date: Wednesday, January 9, 2013, 9:14 AM > Hi, > > On Wed, 9 Jan 2013 05:40:13 -0800 (PST) > Barney Cordoba <barney_cordoba@yahoo.com> > wrote: > > > --- On Wed, 1/9/13, Erich Dollansky <erichsfreebsdlist@alogt.com> > > wrote: > > > From: Erich Dollansky <erichsfreebsdlist@alogt.com> > > > Subject: Re: To SMP or not to SMP > > > To: "Mark Atkinson" <atkin901@gmail.com> > > > Cc: freebsd-net@freebsd.org > > > Date: Wednesday, January 9, 2013, 1:01 AM > > > Hi, > > > > > > On Tue, 08 Jan 2013 08:29:51 -0800 > > > Mark Atkinson <atkin901@gmail.com> > > > wrote: > > > > > > > -----BEGIN PGP SIGNED MESSAGE----- > > > > Hash: SHA1 > > > > > > > > On 01/07/2013 18:25, Barney Cordoba wrote: > > > > > I have a situation where I have to run > 9.1 on an > > > old single core > > > > > box. Does anyone have a handle on > whether it's > > > better to build a > > > > > non SMP kernel or to just use a standard > SMP build > > > with just the > > > > > one core? Thanks. > > > > > > > > You can build a SMP kernel, but you'll get > better > > > performance (in my > > > > experience) with SCHED_4BSD on single cpu > than with > > > ULE. > > > > > > > I would not say so. The machine behaves different > with the > > > two > > > schedulers. It depends mostly what you want to do > with the > > > machine. I > > > forgot which scheduler I finally left in the > single CPU > > > kernel. > > > > > > Erich > > > > 4BSD runs pretty well with an SMP kernel. I can test > ULE and compare > > easily. A no SMP kernel is problematic as the igb > driver doesn't seem > > to work and my onboard NICs are, sadly, igb. > > > this is bad luck. I know of the kernels as I have had SMP > and single > CPU machines since 4.x times. > > > Rather than say "depends what you want to do", perhaps > an explanation > > of which cases you might choose one or the other would > be helpful. > > > > So can anyone in the know confirm that the kernel > really isn't smart > > enough to know there there's only 1 core so that most > of the SMP > > The kernel does not think like this. It is a fixed program > flow. > > > "overhead" is avoided? It seems to me that SMP > scheduling should only > > be enabled if there is more than 1 core as part of the > scheduler > > initialization. Its arrogant indeed to assume that just > because SMP > > support is compiled in that there are multiple cores. > > I compile my own kernels and set the parameters as needed. > > Erich > This explanation defies the possibility of a GENERIC kernel, which of course is an important element of a GPOS. Its too bad that smp support can't be done with logic rather than a kernel option. The big thing I see is the use of legacy interrupts vs msix. Its not like flipping off SMP support only changes the scheduler behavior. BC
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