x86,perf: Unmask LVTPC only if we have APIC supported
in [Kernel]
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From: Ingo Molnar on 13 Mar 2010 07:30 * Cyrill Gorcunov <gorcunov(a)openvz.org> wrote: > Ingo reported > | > | There's a build failure on -tip with the P4 driver, on UP 32-bit, if > | PERF_EVENTS is enabled but UP_APIC is disabled: > | > | arch/x86/built-in.o: In function `p4_pmu_handle_irq': > | perf_event.c:(.text+0xa756): undefined reference to `apic' > | perf_event.c:(.text+0xa76e): undefined reference to `apic' > | > > So we have to unmask LVTPC only if we're configured to have one. > > Reported-by: Ingo Molnar <mingo(a)elte.hu> > CC: Lin Ming <ming.m.lin(a)intel.com> > CC: Peter Zijlstra <peterz(a)infradead.org> > Signed-off-by: Cyrill Gorcunov <gorcunov(a)openvz.org> > --- > arch/x86/kernel/cpu/perf_event_p4.c | 2 ++ > 1 file changed, 2 insertions(+) > > Index: linux-2.6.git/arch/x86/kernel/cpu/perf_event_p4.c > ===================================================================== > --- linux-2.6.git.orig/arch/x86/kernel/cpu/perf_event_p4.c > +++ linux-2.6.git/arch/x86/kernel/cpu/perf_event_p4.c > @@ -365,8 +365,10 @@ static int p4_pmu_handle_irq(struct pt_r > } > > if (handled) { > +#ifdef CONFIG_X86_LOCAL_APIC > /* p4 quirk: unmask it again */ > apic_write(APIC_LVTPC, apic_read(APIC_LVTPC) & ~APIC_LVT_MASKED); > +#endif > inc_irq_stat(apic_perf_irqs); This ugly #ifdef looks like a workaround though. Why doesnt apic_write() map to nothing in that case? Ingo -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
From: Cyrill Gorcunov on 13 Mar 2010 07:40 On Sat, Mar 13, 2010 at 01:24:32PM +0100, Ingo Molnar wrote: > > * Cyrill Gorcunov <gorcunov(a)openvz.org> wrote: > > > Ingo reported > > | > > | There's a build failure on -tip with the P4 driver, on UP 32-bit, if > > | PERF_EVENTS is enabled but UP_APIC is disabled: > > | > > | arch/x86/built-in.o: In function `p4_pmu_handle_irq': > > | perf_event.c:(.text+0xa756): undefined reference to `apic' > > | perf_event.c:(.text+0xa76e): undefined reference to `apic' > > | > > > > So we have to unmask LVTPC only if we're configured to have one. > > > > Reported-by: Ingo Molnar <mingo(a)elte.hu> > > CC: Lin Ming <ming.m.lin(a)intel.com> > > CC: Peter Zijlstra <peterz(a)infradead.org> > > Signed-off-by: Cyrill Gorcunov <gorcunov(a)openvz.org> > > --- > > arch/x86/kernel/cpu/perf_event_p4.c | 2 ++ > > 1 file changed, 2 insertions(+) > > > > Index: linux-2.6.git/arch/x86/kernel/cpu/perf_event_p4.c > > ===================================================================== > > --- linux-2.6.git.orig/arch/x86/kernel/cpu/perf_event_p4.c > > +++ linux-2.6.git/arch/x86/kernel/cpu/perf_event_p4.c > > @@ -365,8 +365,10 @@ static int p4_pmu_handle_irq(struct pt_r > > } > > > > if (handled) { > > +#ifdef CONFIG_X86_LOCAL_APIC > > /* p4 quirk: unmask it again */ > > apic_write(APIC_LVTPC, apic_read(APIC_LVTPC) & ~APIC_LVT_MASKED); > > +#endif > > inc_irq_stat(apic_perf_irqs); > > This ugly #ifdef looks like a workaround though. Why doesnt apic_write() map > to nothing in that case? > > Ingo > It is. I mean -- it maps to nothing if apic is disabled. But the scenario is that no apic configured at all. Actually I wonder how this code is supposed to work without apic support. Pehpaps better to make a p4 quirk helper here, since #ifdef at this point looks ugly indeed. Don't apply it then. Will back with other solution. -- Cyrill -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
From: Ingo Molnar on 13 Mar 2010 07:50 * Cyrill Gorcunov <gorcunov(a)gmail.com> wrote: > On Sat, Mar 13, 2010 at 01:24:32PM +0100, Ingo Molnar wrote: > > > > * Cyrill Gorcunov <gorcunov(a)openvz.org> wrote: > > > > > Ingo reported > > > | > > > | There's a build failure on -tip with the P4 driver, on UP 32-bit, if > > > | PERF_EVENTS is enabled but UP_APIC is disabled: > > > | > > > | arch/x86/built-in.o: In function `p4_pmu_handle_irq': > > > | perf_event.c:(.text+0xa756): undefined reference to `apic' > > > | perf_event.c:(.text+0xa76e): undefined reference to `apic' > > > | > > > > > > So we have to unmask LVTPC only if we're configured to have one. > > > > > > Reported-by: Ingo Molnar <mingo(a)elte.hu> > > > CC: Lin Ming <ming.m.lin(a)intel.com> > > > CC: Peter Zijlstra <peterz(a)infradead.org> > > > Signed-off-by: Cyrill Gorcunov <gorcunov(a)openvz.org> > > > --- > > > arch/x86/kernel/cpu/perf_event_p4.c | 2 ++ > > > 1 file changed, 2 insertions(+) > > > > > > Index: linux-2.6.git/arch/x86/kernel/cpu/perf_event_p4.c > > > ===================================================================== > > > --- linux-2.6.git.orig/arch/x86/kernel/cpu/perf_event_p4.c > > > +++ linux-2.6.git/arch/x86/kernel/cpu/perf_event_p4.c > > > @@ -365,8 +365,10 @@ static int p4_pmu_handle_irq(struct pt_r > > > } > > > > > > if (handled) { > > > +#ifdef CONFIG_X86_LOCAL_APIC > > > /* p4 quirk: unmask it again */ > > > apic_write(APIC_LVTPC, apic_read(APIC_LVTPC) & ~APIC_LVT_MASKED); > > > +#endif > > > inc_irq_stat(apic_perf_irqs); > > > > This ugly #ifdef looks like a workaround though. Why doesnt apic_write() map > > to nothing in that case? > > > > Ingo > > > > It is. I mean -- it maps to nothing if apic is disabled. But the scenario is > that no apic configured at all. Actually I wonder how this code is supposed > to work without apic support. > > Pehpaps better to make a p4 quirk helper here, since #ifdef at this point > looks ugly indeed. > > Don't apply it then. Will back with other solution. 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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
From: Cyrill Gorcunov on 13 Mar 2010 08:50 On Sat, Mar 13, 2010 at 01:40:36PM +0100, Ingo Molnar wrote: > > * Cyrill Gorcunov <gorcunov(a)gmail.com> wrote: > > > On Sat, Mar 13, 2010 at 01:24:32PM +0100, Ingo Molnar wrote: > > > > > > * Cyrill Gorcunov <gorcunov(a)openvz.org> wrote: > > > > > > > Ingo reported > > > > | > > > > | There's a build failure on -tip with the P4 driver, on UP 32-bit, if > > > > | PERF_EVENTS is enabled but UP_APIC is disabled: > > > > | > > > > | arch/x86/built-in.o: In function `p4_pmu_handle_irq': > > > > | perf_event.c:(.text+0xa756): undefined reference to `apic' > > > > | perf_event.c:(.text+0xa76e): undefined reference to `apic' > > > > | > > > > > > > > So we have to unmask LVTPC only if we're configured to have one. > > > > > > > > Reported-by: Ingo Molnar <mingo(a)elte.hu> > > > > CC: Lin Ming <ming.m.lin(a)intel.com> > > > > CC: Peter Zijlstra <peterz(a)infradead.org> > > > > Signed-off-by: Cyrill Gorcunov <gorcunov(a)openvz.org> > > > > --- > > > > arch/x86/kernel/cpu/perf_event_p4.c | 2 ++ > > > > 1 file changed, 2 insertions(+) > > > > > > > > Index: linux-2.6.git/arch/x86/kernel/cpu/perf_event_p4.c > > > > ===================================================================== > > > > --- linux-2.6.git.orig/arch/x86/kernel/cpu/perf_event_p4.c > > > > +++ linux-2.6.git/arch/x86/kernel/cpu/perf_event_p4.c > > > > @@ -365,8 +365,10 @@ static int p4_pmu_handle_irq(struct pt_r > > > > } > > > > > > > > if (handled) { > > > > +#ifdef CONFIG_X86_LOCAL_APIC > > > > /* p4 quirk: unmask it again */ > > > > apic_write(APIC_LVTPC, apic_read(APIC_LVTPC) & ~APIC_LVT_MASKED); > > > > +#endif > > > > inc_irq_stat(apic_perf_irqs); > > > > > > This ugly #ifdef looks like a workaround though. Why doesnt apic_write() map > > > to nothing in that case? > > > > > > Ingo > > > > > > > It is. I mean -- it maps to nothing if apic is disabled. But the scenario is > > that no apic configured at all. Actually I wonder how this code is supposed > > to work without apic support. > > > > Pehpaps better to make a p4 quirk helper here, since #ifdef at this point > > looks ugly indeed. > > > > Don't apply it then. Will back with other solution. > > 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? -- Cyrill -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
From: Ingo Molnar on 13 Mar 2010 09:00 * Cyrill Gorcunov <gorcunov(a)gmail.com> wrote: > On Sat, Mar 13, 2010 at 01:40:36PM +0100, Ingo Molnar wrote: > > > > * Cyrill Gorcunov <gorcunov(a)gmail.com> wrote: > > > > > On Sat, Mar 13, 2010 at 01:24:32PM +0100, Ingo Molnar wrote: > > > > > > > > * Cyrill Gorcunov <gorcunov(a)openvz.org> wrote: > > > > > > > > > Ingo reported > > > > > | > > > > > | There's a build failure on -tip with the P4 driver, on UP 32-bit, if > > > > > | PERF_EVENTS is enabled but UP_APIC is disabled: > > > > > | > > > > > | arch/x86/built-in.o: In function `p4_pmu_handle_irq': > > > > > | perf_event.c:(.text+0xa756): undefined reference to `apic' > > > > > | perf_event.c:(.text+0xa76e): undefined reference to `apic' > > > > > | > > > > > > > > > > So we have to unmask LVTPC only if we're configured to have one. > > > > > > > > > > Reported-by: Ingo Molnar <mingo(a)elte.hu> > > > > > CC: Lin Ming <ming.m.lin(a)intel.com> > > > > > CC: Peter Zijlstra <peterz(a)infradead.org> > > > > > Signed-off-by: Cyrill Gorcunov <gorcunov(a)openvz.org> > > > > > --- > > > > > arch/x86/kernel/cpu/perf_event_p4.c | 2 ++ > > > > > 1 file changed, 2 insertions(+) > > > > > > > > > > Index: linux-2.6.git/arch/x86/kernel/cpu/perf_event_p4.c > > > > > ===================================================================== > > > > > --- linux-2.6.git.orig/arch/x86/kernel/cpu/perf_event_p4.c > > > > > +++ linux-2.6.git/arch/x86/kernel/cpu/perf_event_p4.c > > > > > @@ -365,8 +365,10 @@ static int p4_pmu_handle_irq(struct pt_r > > > > > } > > > > > > > > > > if (handled) { > > > > > +#ifdef CONFIG_X86_LOCAL_APIC > > > > > /* p4 quirk: unmask it again */ > > > > > apic_write(APIC_LVTPC, apic_read(APIC_LVTPC) & ~APIC_LVT_MASKED); > > > > > +#endif > > > > > inc_irq_stat(apic_perf_irqs); > > > > > > > > This ugly #ifdef looks like a workaround though. Why doesnt apic_write() map > > > > to nothing in that case? > > > > > > > > Ingo > > > > > > > > > > It is. I mean -- it maps to nothing if apic is disabled. But the scenario is > > > that no apic configured at all. Actually I wonder how this code is supposed > > > to work without apic support. > > > > > > Pehpaps better to make a p4 quirk helper here, since #ifdef at this point > > > looks ugly indeed. > > > > > > Don't apply it then. Will back with other solution. > > > > 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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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