lkml.org 
[lkml]   [2010]   [Mar]   [13]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH] x86,perf: Unmask LVTPC only if we have APIC supported
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


\
 
 \ /
  Last update: 2010-03-13 15:11    [W:0.192 / U:0.056 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site