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From: Cyrill Gorcunov on 13 Mar 2010 09:10
On Sat, Mar 13, 2010 at 02:50:22PM +0100, Ingo Molnar wrote:
[ ... ]
> > >
> > > apic_write() is really just equivalent to a spin_lock() on UP without
> > > UP_IOAPIC set - it should do nothing. So if it does something and fails the
> > > build, then that should be fixed - not the P4 PMU code.
> > >
> > > Ingo
> > >
> >
> > Looking at code a bit and config deps I think the former proposal with
> > #ifdef is minimal (in amount of changes) and sufficient. perf_event.c
> > uses #ifdef CONFIG_X86_LOCAL_APIC for the very same reason.
> >
> > The former issue with config dependencies is that we may need to compile
> > perf_event.c without CONFIG_LOCAL_APIC support at all (and this is a case
> > for which you've posted the config). CONFIG_LOCAL_APIC deps on X86_UP_APIC,
> > the config has no X86_UP_APIC support and as result -- no CONFIG_LOCAL_APIC
> > and no apic.o compiled.
> >
> > So, as expected, no apic_write/read and friends there. We may introduce
> > apic_write/read weak(s) but this would only mess the code more and would
> > smell unpleasant I think :) .
> >
> > All-in-once: unresolved external symbol here, which could be fixed either by
> > introducing dummy symbol, or conditional compilation. I think the second is
> > preferred if the issue is just one line code.
> >
> > Or you mean something different and I took a wrong mind-path?
>
> Well it's not just one line of code as (like you mentioned) perf_event.c is
> affected as well.
>
> Introducing a dummy (NOP) placeholder method is what we are doing in all the
> other cases (such as spin_lock()), we dont pollute the kernel with #ifdefs.
>
> Ingo
>

ok, understood what you mean. will back with patch.

-- Cyrill
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From: Cyrill Gorcunov on 13 Mar 2010 10:10
On Sat, Mar 13, 2010 at 02:50:22PM +0100, Ingo Molnar wrote:
....
> > All-in-once: unresolved external symbol here, which could be fixed either by
> > introducing dummy symbol, or conditional compilation. I think the second is
> > preferred if the issue is just one line code.
> >
> > Or you mean something different and I took a wrong mind-path?
>
> Well it's not just one line of code as (like you mentioned) perf_event.c is
> affected as well.
>
> Introducing a dummy (NOP) placeholder method is what we are doing in all the
> other cases (such as spin_lock()), we dont pollute the kernel with #ifdefs.
>
> Ingo
>

ok, Ingo, this will consume some time. Could you pick up the original patch
just for now (so that testing builds will not fail), I'll back to this task
tomorrow or at Monday. OK?

-- Cyrill
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