Date: Wed, 27 Oct 2004 14:47:32 -0400 From: Mike Tancsa <mike@sentex.net> To: John Baldwin <jhb@FreeBSD.org>, freebsd-current@FreeBSD.org Subject: Re: device apic on a single processor machine Message-ID: <6.1.2.0.0.20041027144023.0952bfb8@64.7.153.2> In-Reply-To: <200410271400.31895.jhb@FreeBSD.org> References: <6.1.2.0.0.20041022113405.08fe2c48@64.7.153.2> <200410271400.31895.jhb@FreeBSD.org>
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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.html) ... So if it provides a cleaner / more stable way to talk to the devices, I will certainly run with it. ---Mike
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