Date: Wed, 9 Jan 2013 21:14:39 +0700 From: Erich Dollansky <erichsfreebsdlist@alogt.com> To: Barney Cordoba <barney_cordoba@yahoo.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: <20130109211439.5b590bf5@X220.ovitrap.com> In-Reply-To: <1357738813.28186.YahooMailClassic@web121601.mail.ne1.yahoo.com> References: <20130109130133.0399a6cc@X220.ovitrap.com> <1357738813.28186.YahooMailClassic@web121601.mail.ne1.yahoo.com>
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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
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