IMC(In-memory Collection Counters) does performance monitoring in
two different modes, i.e accumulation mode(core-imc and thread-imc events),
and trace mode(trace-imc events). A cpu thread can either be in
accumulation-mode or trace-mode at a time and this is done via the LDBAR
register in POWER architecture. The current design does not address the
races between thread-imc and trace-imc events.
Patch implements a global id and lock to avoid the races between
core, trace and thread imc events. With this global id-lock
implementation, the system can either run core, thread or trace imc
events at a time. i.e. to run any core-imc events, thread/trace imc events
should not be enabled/monitored.
Signed-off-by: Anju T Sudhakar
---
Changes from v3->v4:
- Added mutex lock for thread, core and trace imc cpu offline path.
Changes from v2->v3:
- Addressed the off-line comments from Michael Ellerman
- Optimized the *_event_init code path for trace, core and thread imc
- Handled the global refc in cpuhotplug scenario
- Re-order the patch series
- Removed the selftest patches and will send as a follow up patch
Changes from v1 -> v2:
- Added self test patches to the series.
---
arch/powerpc/perf/imc-pmu.c | 173 +++-
1 file changed, 149 insertions(+), 24 deletions(-)
diff --git a/arch/powerpc/perf/imc-pmu.c b/arch/powerpc/perf/imc-pmu.c
index cb50a9e1fd2d..eb82dda884e5 100644
--- a/arch/powerpc/perf/imc-pmu.c
+++ b/arch/powerpc/perf/imc-pmu.c
@@ -44,6 +44,16 @@ static DEFINE_PER_CPU(u64 *, trace_imc_mem);
static struct imc_pmu_ref *trace_imc_refc;
static int trace_imc_mem_size;
+/*
+ * Global data structure used to avoid races between thread,
+ * core and trace-imc
+ */
+static struct imc_pmu_ref imc_global_refc = {
+ .lock = __MUTEX_INITIALIZER(imc_global_refc.lock),
+ .id = 0,
+ .refc = 0,
+};
+
static struct imc_pmu *imc_event_to_pmu(struct perf_event *event)
{
return container_of(event->pmu, struct imc_pmu, pmu);
@@ -698,6 +708,16 @@ static int ppc_core_imc_cpu_offline(unsigned int cpu)
return -EINVAL;
ref->refc = 0;
+ /*
+* Reduce the global reference count, if this is the
+* last cpu in this core and core-imc event running
+* in this cpu.
+*/
+ mutex_lock(_global_refc.lock);
+ if (imc_global_refc.id == IMC_DOMAIN_CORE)
+ imc_global_refc.refc--;
+
+ mutex_unlock(_global_refc.lock);
}
return 0;
}
@@ -710,6 +730,23 @@ static int core_imc_pmu_cpumask_init(void)
ppc_core_imc_cpu_offline);
}
+static void reset_global_refc(struct perf_event *event)
+{
+ mutex_lock(_global_refc.lock);
+ imc_global_refc.refc--;
+
+ /*
+* If no other thread is running any
+* event for this domain(thread/core/trace),
+* set the global id to zero.
+*/
+ if (imc_global_refc.refc <= 0) {
+ imc_global_refc.refc = 0;
+ imc_global_refc.id = 0;
+ }
+ mutex_unlock(_global_refc.lock);
+}
+
static void core_imc_counters_release(struct perf_event *event)
{
int rc, core_id;
@@ -759,6 +796,8 @@ static void core_imc_counters_release(struct perf_event
*event)
ref->refc = 0;
}
mutex_unlock(>lock);
+
+ reset_global_refc(event);
}
static int core_imc_event_init(struct perf_event *event)
@@ -819,6 +858,29 @@ static int core_imc_event_init(struct perf_event *event)
++ref->refc;
mutex_unlock(>lock);
+ /*
+* Since the system can run either in accumulation or trace-mode
+* of IMC at a time, core-imc events are allowed only if no other
+* trace/thread imc events are enabled/monitored.
+*
+* Take the global lock, and check the refc.id
+* to know whether any other trace/thread imc
+* events are running.
+*/
+ mutex_lock(_global_refc.lock);
+ if (imc_global_refc.id == 0 || imc_global_refc.id == IMC_DOMAIN_CORE) {
+ /*
+* No other trace/thread imc events are running in
+* the system, so set the refc.id to core-imc.
+*/
+ imc_global_refc.id = IMC_DOMAIN_CORE;
+ imc_global_refc.refc++;
+ } else {
+ mutex_unlock(_global_refc.lock);
+ return -EBUSY;
+ }
+ mutex_unlock(_global_refc.lock);
+
event->hw.event_base = (u64)pcmi->vbase + (config &
IMC_EVENT_OFFSET_MASK);
event->destroy = core_imc_counters_release;
return 0;
@@ -877,7 +939,23 @@ static int ppc_thread_imc_cpu_online(unsigned int cpu)
static int ppc_thread_imc_cpu_offline(unsigned int cpu)
{
-
