Re: 2.6.27rc1 cannot boot more than 8CPUs

Ingo Molnar
2008-08-11T20:08:37Z

* Yinghai Lu <yhlu.kernel@gmail.com> wrote:

> On Mon, Aug 11, 2008 at 12:59 PM, Ingo Molnar <mingo@elte.hu> wrote:
> >
> > * Jeff Chua <jeff.chua.linux@gmail.com> wrote:
> >
> >> On Wed, Aug 6, 2008 at 2:42 PM, Jeff Chua <jeff.chua.linux@gmail.com> wrote:
> >> > On Wed, Aug 6, 2008 at 2:01 PM, Linus Torvalds
> >> > <torvalds@linux-foundation.org> wrote:
> >> >> One trivial thing to try would be to just bisect it. I assume 2.6.26 is
> >> > Bisecting now.
> >>
> >> Thanks to all the great helpful suggestions from everyone, and this
> >> turns out that I just need to enable the following switches, so I
> >> didn't bisect further, and since it's first machine that I've tried
> >> with more than 8 CPUs so I wasn't sure whether 2.6.16 has the same
> >> problem, but if you wish, I could give 2.6.16 a try.
> >>
> >> > CONFIG_X86_GENERICARCH=y
> >> > CONFIG_X86_BIGSMP=y
> >>
> >> Thank you all for the great linux kernel!
> >
> > i still consider a silent boot hang a bug we need to fix.
> >
> > bigsmp might be required to have all cpus available on your box, but the
> > kernel is still supposed to transparently fall back to less CPUs (and
> > print a warning) if it cannot do that.
> >
> in setup.c::setup_arch() after go over with madt or mptable
>
> #if defined(CONFIG_SMP) && defined(CONFIG_X86_PC) && defined(CONFIG_X86_32)
> if (def_to_bigsmp)
> printk(KERN_WARNING "More than 8 CPUs detected and "
> "CONFIG_X86_PC cannot handle it.\nUse "
> "CONFIG_X86_GENERICARCH or
> CONFIG_X86_BIGSMP.\n"); ===> here need to change "or" to "and"
> #endif
>
> or just panic here? because screen scroll to pass it, and user will
> not notice that...

a panic is better but still quite rude and doesnt give a user a system
under which he can build an even greater kernel [after having discovered
the warning in the syslog] ;-)

best would be to use as many CPUs as we can support, and skip the rest
and boot up fine. (and print the warning prominently - the user does not
make maximum use of available physical resources)

Ingo