Re: Patch?: linux-2.5.41 multiprocessor vs. CONFIG_X86_TSC

James Bottomley
2002-10-10T16:47:11Z

On Thu, Oct 10, 2002 at 05:02:12AM -0700, Adam J. Richter wrote:
> 2. Are there x86 multiprocessors that Linux runs on that lack the
> Time Stamp Counter feature? If so, I would welcome any
> suggestions or requests on how best to fix arch/i386/smpboot.c.

> It's useless on NUMA-Q. The assumption is that they're synchronized
> and it's infeasible to synchronize them without elaborate fixup
> machinery on the things, which can at best fake it.

> wrt. Voyager et al. James Bottomley is the right person to ask.

> As far as active development on NUMA-Q and x440 in the timer arena
> goes, John Stultz knows best.

Voyager is in the same boat as NUMA-Q. The machines can have up to eight CPU
card slots and each slot can take up to a quad CPU card (with the clock
generator on the CPU card) so TSCs cannot synchronise accross the quads.
Worse, for voyager, the CPUs and clocks can be radically different frequencies
(I run a dual quad system here with one quad at 100MHz and one at 166MHz)

Voyager can also run with ancient dyad 486 CPU cards (I still have some) which
do lack the TSC feature entirely. However, I don't use the smpboot.c file to
boot with, so if you want changes in there that's fine by me, I'll just hook
the voyager boot sequence into them.

James