perf_counter: powerpc: Enable use of software counters on 32-bit powerpc

This enables the perf_counter subsystem on 32-bit powerpc.  Since we
don't have any support for hardware counters on 32-bit powerpc yet,
only software counters can be used.

Besides selecting HAVE_PERF_COUNTERS for 32-bit powerpc as well as
64-bit, the main thing this does is add an implementation of
set_perf_counter_pending().  This needs to arrange for
perf_counter_do_pending() to be called when interrupts are enabled.
Rather than add code to local_irq_restore as 64-bit does, the 32-bit
set_perf_counter_pending() generates an interrupt by setting the
decrementer to 1 so that a decrementer interrupt will become pending
in 1 or 2 timebase ticks (if a decrementer interrupt isn't already
pending).  When interrupts are enabled, timer_interrupt() will be
called, and some new code in there calls perf_counter_do_pending().
We use a per-cpu array of flags to indicate whether we need to call
perf_counter_do_pending() or not.

This introduces a couple of new Kconfig symbols: PPC_HAVE_PMU_SUPPORT,
which is selected by processor families for which we have hardware PMU
support (currently only PPC64), and PPC_PERF_CTRS, which enables the
powerpc-specific perf_counter back-end.

Signed-off-by: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: linuxppc-dev@ozlabs.org
Cc: benh@kernel.crashing.org
LKML-Reference: <19000.55404.103840.393470@cargo.ozlabs.ibm.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

2 files changed, 28 insertions, 3 deletions

diff --git a/arch/powerpc/kernel/Makefile b/arch/powerpc/kernel/Makefile
index 612b0c4dc26d..c5f93f061927 100644
--- a/arch/powerpc/kernel/Makefile
+++ b/arch/powerpc/kernel/Makefile
@@ -95,9 +95,9 @@ obj64-$(CONFIG_AUDIT)		+= compat_audit.o
 
 obj-$(CONFIG_DYNAMIC_FTRACE)    += ftrace.o
 obj-$(CONFIG_FUNCTION_GRAPH_TRACER)     += ftrace.o
-obj-$(CONFIG_PERF_COUNTERS)     += perf_counter.o power4-pmu.o ppc970-pmu.o \
-                                   power5-pmu.o power5+-pmu.o power6-pmu.o \
-                                   power7-pmu.o
+obj-$(CONFIG_PPC_PERF_CTRS)     += perf_counter.o
+obj64-$(CONFIG_PPC_PERF_CTRS)   += power4-pmu.o ppc970-pmu.o power5-pmu.o \
+                                   power5+-pmu.o power6-pmu.o power7-pmu.o
 
 obj-$(CONFIG_8XX_MINIMAL_FPEMU) += softemu8xx.o
 
diff --git a/arch/powerpc/kernel/time.c b/arch/powerpc/kernel/time.c
index 15391c2ab013..eae4511ceeac 100644
--- a/arch/powerpc/kernel/time.c
+++ b/arch/powerpc/kernel/time.c
@@ -53,6 +53,7 @@
 #include <linux/posix-timers.h>
 #include <linux/irq.h>
 #include <linux/delay.h>
+#include <linux/perf_counter.h>
 
 #include <asm/io.h>
 #include <asm/processor.h>
@@ -525,6 +526,26 @@ void __init iSeries_time_init_early(void)
 }
 #endif /* CONFIG_PPC_ISERIES */
 
+#if defined(CONFIG_PERF_COUNTERS) && defined(CONFIG_PPC32)
+DEFINE_PER_CPU(u8, perf_counter_pending);
+
+void set_perf_counter_pending(void)
+{
+        get_cpu_var(perf_counter_pending) = 1;
+        set_dec(1);
+        put_cpu_var(perf_counter_pending);
+}
+
+#define test_perf_counter_pending()     __get_cpu_var(perf_counter_pending)
+#define clear_perf_counter_pending()    __get_cpu_var(perf_counter_pending) = 0
+
+#else  /* CONFIG_PERF_COUNTERS && CONFIG_PPC32 */
+
+#define test_perf_counter_pending()     0
+#define clear_perf_counter_pending()
+
+#endif /* CONFIG_PERF_COUNTERS && CONFIG_PPC32 */
+
 /*
  * For iSeries shared processors, we have to let the hypervisor
  * set the hardware decrementer.  We set a virtual decrementer
@@ -551,6 +572,10 @@ void timer_interrupt(struct pt_regs * regs)
         set_dec(DECREMENTER_MAX);
 
 #ifdef CONFIG_PPC32
+        if (test_perf_counter_pending()) {
+                clear_perf_counter_pending();
+                perf_counter_do_pending();
+        }
         if (atomic_read(&ppc_n_lost_interrupts) != 0)
                 do_IRQ(regs);
 #endif