Date: Wed, 27 Oct 2004 15:09:57 -0400 From: John Baldwin <jhb@FreeBSD.org> To: Mike Tancsa <mike@sentex.net> Cc: freebsd-current@FreeBSD.org Subject: Re: device apic on a single processor machine Message-ID: <200410271509.57177.jhb@FreeBSD.org> In-Reply-To: <6.1.2.0.0.20041027144023.0952bfb8@64.7.153.2> References: <6.1.2.0.0.20041022113405.08fe2c48@64.7.153.2> <200410271400.31895.jhb@FreeBSD.org> <6.1.2.0.0.20041027144023.0952bfb8@64.7.153.2>
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On Wednesday 27 October 2004 02:47 pm, Mike Tancsa wrote: > At 02:00 PM 27/10/2004, John Baldwin wrote: > >On Friday 22 October 2004 11:40 am, Mike Tancsa wrote: > > > When moving from RELENG_4 to RELENG_5, I noticed that in GENERIC, the > > > options > > > > > > options SMP # Symmetric MultiProcessor Kernel > > > device apic # I/O APIC > > > > > > are enabled by default. Going forward, is this the best thing to leave > > > in my default kernel on a uniprocessor machine ? I am not using the > > > ULE scheduler either and have hyperthreading disabled in the BIOS. > > > > > > I did a search on google, and in 2003 it was said not to having either > > > on a single processor machine but its not clear if this is no longer > > > the case. > > > >You do want to drop SMP. As far as 'apic', that is less clear. If you > > have lots of PCI devices that share interrupts for the !apic case and you > > do lots of interrupt intensive tasks, then 'device apic' might help. > > There may also be cases where it hurts. There have been reports that > > access to the apic registers for things like masking sources takes longer > > than on the 8259As. > > Thanks for the feedback. I guess my question is, what constitutes "lots" ? > Typically, I strip down boxes to their bare min hardware wise so in most > cases, I dont have anything sharing interrupts (I usually turn off USB > which is the most gratuitous). But I do have a POS app that needs USB as > well as 2 PCI serial cards. In this case, I do have a lot of shared > interrupts. However, it almost never is CPU bound or has an interrupt rate > higher than 10-20%. In this case, stability is more important to me. I > have run into a number of cases where there are interrupt storms (e.g > http://lists.freebsd.org/pipermail/freebsd-current/2004-September/036967.ht >ml) > > ... So if it provides a cleaner / more stable way to talk to the devices, I > will certainly run with it. I would try it both ways and see if one works better than the other. -- John Baldwin <jhb@FreeBSD.org> <>< http://www.FreeBSD.org/~jhb/ "Power Users Use the Power to Serve" = http://www.FreeBSD.org
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