[PATCH AUTOSEL 5.4 224/330] powerpc/perf: Implement a global lock to avoid races between trace, core and thread imc events.

Sasha Levin
2020-09-18T03:00:09Z

From: Anju T Sudhakar <anju@linux.vnet.ibm.com>

[ Upstream commit a36e8ba60b991d563677227f172db69e030797e6 ]

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 <anju@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20200313055238.8656-1-anju@linux.vnet.ibm.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
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 cb50a9e1fd2d7..eb82dda884e51 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(&imc_global_refc.lock);
+ if (imc_global_refc.id == IMC_DOMAIN_CORE)
+ imc_global_refc.refc--;
+
+ mutex_unlock(&imc_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(&imc_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(&imc_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(&ref->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(&ref->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(&imc_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(&imc_global_refc.lock);
+ return -EBUSY;
+ }
+ mutex_unlock(&imc_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)
{
- mtspr(SPRN_LDBAR, 0);
+ /*
+ * Set the bit 0 of LDBAR to zero.
+ *
+ * If bit 0 of LDBAR is unset, it will stop posting
+ * the counter data to memory.
+ * For thread-imc, bit 0 of LDBAR will be set to 1 in the
+ * event_add function. So reset this bit here, to stop the updates
+ * to memory in the cpu_offline path.
+ */
+ mtspr(SPRN_LDBAR, (mfspr(SPRN_LDBAR) & (~(1UL << 63))));
+
+ /* Reduce the refc if thread-imc event running on this cpu */
+ mutex_lock(&imc_global_refc.lock);
+ if (imc_global_refc.id == IMC_DOMAIN_THREAD)
+ imc_global_refc.refc--;
+ mutex_unlock(&imc_global_refc.lock);
+
return 0;
}

@@ -916,7 +994,22 @@ static int thread_imc_event_init(struct perf_event *event)
if (!target)
return -EINVAL;

+ mutex_lock(&imc_global_refc.lock);
+ /*
+ * Check if any other trace/core imc events are running in the
+ * system, if not set the global id to thread-imc.
+ */
+ if (imc_global_refc.id == 0 || imc_global_refc.id == IMC_DOMAIN_THREAD) {
+ imc_global_refc.id = IMC_DOMAIN_THREAD;
+ imc_global_refc.refc++;
+ } else {
+ mutex_unlock(&imc_global_refc.lock);
+ return -EBUSY;
+ }
+ mutex_unlock(&imc_global_refc.lock);
+
event->pmu->task_ctx_nr = perf_sw_context;
+ event->destroy = reset_global_refc;
return 0;
}

@@ -1063,10 +1156,12 @@ static void thread_imc_event_del(struct perf_event *event, int flags)
int core_id;
struct imc_pmu_ref *ref;

- mtspr(SPRN_LDBAR, 0);
-
core_id = smp_processor_id() / threads_per_core;
ref = &core_imc_refc[core_id];
+ if (!ref) {
+ pr_debug("imc: Failed to get event reference count\n");
+ return;
+ }

mutex_lock(&ref->lock);
ref->refc--;
@@ -1082,6 +1177,10 @@ static void thread_imc_event_del(struct perf_event *event, int flags)
ref->refc = 0;
}
mutex_unlock(&ref->lock);
+
+ /* Set bit 0 of LDBAR to zero, to stop posting updates to memory */
+ mtspr(SPRN_LDBAR, (mfspr(SPRN_LDBAR) & (~(1UL << 63))));
+
/*
* Take a snapshot and calculate the delta and update
* the event counter values.
@@ -1133,7 +1232,18 @@ static int ppc_trace_imc_cpu_online(unsigned int cpu)

static int ppc_trace_imc_cpu_offline(unsigned int cpu)
{
- mtspr(SPRN_LDBAR, 0);
+ /*
+ * No need to set bit 0 of LDBAR to zero, as
+ * it is set to zero for imc trace-mode
+ *
+ * Reduce the refc if any trace-imc event running
+ * on this cpu.
+ */
+ mutex_lock(&imc_global_refc.lock);
+ if (imc_global_refc.id == IMC_DOMAIN_TRACE)
+ imc_global_refc.refc--;
+ mutex_unlock(&imc_global_refc.lock);
+
return 0;
}

@@ -1226,15 +1336,14 @@ static int trace_imc_event_add(struct perf_event *event, int flags)
local_mem = get_trace_imc_event_base_addr();
ldbar_value = ((u64)local_mem & THREAD_IMC_LDBAR_MASK) | TRACE_IMC_ENABLE;

- if (core_imc_refc)
- ref = &core_imc_refc[core_id];
+ /* trace-imc reference count */
+ if (trace_imc_refc)
+ ref = &trace_imc_refc[core_id];
if (!ref) {
- /* If core-imc is not enabled, use trace-imc reference count */
- if (trace_imc_refc)
- ref = &trace_imc_refc[core_id];
- if (!ref)
- return -EINVAL;
+ pr_debug("imc: Failed to get the event reference count\n");
+ return -EINVAL;
}
+
mtspr(SPRN_LDBAR, ldbar_value);
mutex_lock(&ref->lock);
if (ref->refc == 0) {
@@ -1242,13 +1351,11 @@ static int trace_imc_event_add(struct perf_event *event, int flags)
get_hard_smp_processor_id(smp_processor_id()))) {
mutex_unlock(&ref->lock);
pr_err("trace-imc: Unable to start the counters for core %d\n", core_id);
- mtspr(SPRN_LDBAR, 0);
return -EINVAL;
}
}
++ref->refc;
mutex_unlock(&ref->lock);
-
return 0;
}

@@ -1274,16 +1381,13 @@ static void trace_imc_event_del(struct perf_event *event, int flags)
int core_id = smp_processor_id() / threads_per_core;
struct imc_pmu_ref *ref = NULL;

- if (core_imc_refc)
- ref = &core_imc_refc[core_id];
+ if (trace_imc_refc)
+ ref = &trace_imc_refc[core_id];
if (!ref) {
- /* If core-imc is not enabled, use trace-imc reference count */
- if (trace_imc_refc)
- ref = &trace_imc_refc[core_id];
- if (!ref)
- return;
+ pr_debug("imc: Failed to get event reference count\n");
+ return;
}
- mtspr(SPRN_LDBAR, 0);
+
mutex_lock(&ref->lock);
ref->refc--;
if (ref->refc == 0) {
@@ -1297,6 +1401,7 @@ static void trace_imc_event_del(struct perf_event *event, int flags)
ref->refc = 0;
}
mutex_unlock(&ref->lock);
+
trace_imc_event_stop(event, flags);
}

@@ -1314,10 +1419,30 @@ static int trace_imc_event_init(struct perf_event *event)
if (event->attr.sample_period == 0)
return -ENOENT;

+ /*
+ * Take the global lock, and make sure
+ * no other thread is running any core/thread imc
+ * events
+ */
+ mutex_lock(&imc_global_refc.lock);
+ if (imc_global_refc.id == 0 || imc_global_refc.id == IMC_DOMAIN_TRACE) {
+ /*
+ * No core/thread imc events are running in the
+ * system, so set the refc.id to trace-imc.
+ */
+ imc_global_refc.id = IMC_DOMAIN_TRACE;
+ imc_global_refc.refc++;
+ } else {
+ mutex_unlock(&imc_global_refc.lock);
+ return -EBUSY;
+ }
+ mutex_unlock(&imc_global_refc.lock);
+
event->hw.idx = -1;
target = event->hw.target;

event->pmu->task_ctx_nr = perf_hw_context;
+ event->destroy = reset_global_refc;
return 0;
}

@@ -1429,10 +1554,10 @@ static void cleanup_all_core_imc_memory(void)
static void thread_imc_ldbar_disable(void *dummy)
{
/*
- * By Zeroing LDBAR, we disable thread-imc
- * updates.
+ * By setting 0th bit of LDBAR to zero, we disable thread-imc
+ * updates to memory.
*/
- mtspr(SPRN_LDBAR, 0);
+ mtspr(SPRN_LDBAR, (mfspr(SPRN_LDBAR) & (~(1UL << 63))));
}

void thread_imc_disable(void)
--
2.25.1