Date: Thu, 26 Jan 2006 07:55:33 -0700 From: Scott Long <scottl@samsco.org> To: John Baldwin <jhb@FreeBSD.org> Cc: Murray Stokely <murray@FreeBSD.org>, cvs-doc@FreeBSD.org, cvs-all@FreeBSD.org, Robert Watson <rwatson@FreeBSD.org>, doc-committers@FreeBSD.org, Ceri Davies <ceri@submonkey.net> Subject: Re: cvs commit: www/en/releases/6.1R todo.sgml Message-ID: <43D8E2E5.5060309@samsco.org> In-Reply-To: <200601260948.21491.jhb@freebsd.org> References: <200601260957.k0Q9vCUn054132@repoman.freebsd.org> <20060126101706.GJ36965@submonkey.net> <20060126122528.E16741@fledge.watson.org> <200601260948.21491.jhb@freebsd.org>
next in thread | previous in thread | raw e-mail | index | archive | help
John Baldwin wrote: > On Thursday 26 January 2006 07:27, Robert Watson wrote: > >>On Thu, 26 Jan 2006, Ceri Davies wrote: >> >>>On Thu, Jan 26, 2006 at 09:57:12AM +0000, Murray Stokely wrote: >>> >>>>murray 2006-01-26 09:57:12 UTC >>>> >>>> FreeBSD doc repository >>>> >>>> Modified files: >>>> en/releases/6.1R todo.sgml >>>> Log: >>>> Add kbdmux and sysinstall smp kernel install items from the ideas page >>>> to the 6.1 Desired Features list. >>> >>>I think it's a little late to mess with sysinstall to that extent for >>>6.1. Sounds like the kind of thing that could sit in -CURRENT for months, >>>but hardly anyone would actually be using it. It seems that the main >>>problem with sysinstall is that hardly any of our developers use it. >>> >>>On to the question: how often does an SMP kernel fail to boot where a UP >>>one might work? I remember that this used to be a problem, but if it's >>>still "too often", can we have just the bits that probe for an mptable >>>(or however we determine that there is more that one processor) in the UP >>>kernel without suffering that instability? >>> >>>What I'm basically asking is how much of the SMP code is really required >>>just to detect MP hardware? >> >>SMP kernels now pretty much universally run on UP systems, thanks to work >>John did a couple of years ago. The problem has historically been a >>performance once: the overhead of all the atomic instructions to run an SMP >>kernel on a UP system is significant. We're working gradually to improve >>that, but it's still quite noticeable. There has been talk of run-time >>compiling/relinking to use different versions of mutexes (and all that), >>but no progress as far as I know. I can't speak to how much information >>the loader has/needs to decide if it should auto-load an SMP kernel. A >>simpler version of the world says that you have an SMP kernel in >>sysinstall, and based on it probing CPUs, it sets the default kernel in the >>install to GENERIC or SMP. > > > Yes, I would very much prefer that the install just use an SMP kernel. Note > that on all the non-i386 architectures we just have SMP on in GENERIC if it > is supported. > SMP kernels still do not universally work on all i386 machines. I know that Alpha and Sparc hardware was designed from the ground up to support SMP, instead of being a bolted on hack like with x86, but that doesn't change the facts of the situation. Despite your work, I don't think it will ever be safe to make SMP be the default on x86. Scott
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?43D8E2E5.5060309>