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
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