Messages in this thread | | | Date | Sat, 13 Mar 2010 17:08:19 +0300 | From | Cyrill Gorcunov <> | Subject | Re: [PATCH] x86,perf: Unmask LVTPC only if we have APIC supported |
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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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