SMP on UP (Was Re: State of the Linux PCI and PCI Hotplug Subsystems for 2.6.16-rc5)

[Ben Collins <bcollins@ubuntu.com>]

On Thu, 2006-03-09 at 15:52 -0500, Lee Revell wrote:
> On Thu, 2006-03-09 at 15:10 -0500, Ben Collins wrote:
> > The difference between our 2.6.15 386 and 686 kernels is actually pretty
> > huge. The 386 is M486, and UP, while our 686 kernel is M686, and SMP.
> > The SMP is also complicated by our use of the SMP-alternatives patch,
> > but I believe I had this user test with this disabled (kernel command
> > line option that leaves all the SMP code intact for testing). It didn't
> > alter the problem. 
> 
> Ubuntu doesn't provide a UP 686 kernel?
> 
> Isn't there a performance hit running an SMP kernel on UP?

This is a little off-topic to the original thread, so trimming CC and
changing subject.

As mentioned above, we have the SMP-alternatives patch, which will
basically convert SMP related code (lock op's and some atomic
operations) to UP, on-the-fly (at boot for the kernel, and at load for
modules). It's not 100% the same as running a UP kernel, but it comes
close enough that it allows us to distribute fewer kernels. This equates
to less load on us and our users.

I don't want to start this whole thread over again, so check back in the
linux-kernel archives for the SMP alternatives patch thread.

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