[PATCH v5 5/8] drm/xe/xe_pmu: Acquire forcewake on event init for engine events
Umesh Nerlige Ramappa
umesh.nerlige.ramappa at intel.com
Tue Feb 11 17:33:32 UTC 2025
On Mon, Feb 10, 2025 at 03:50:00PM +0530, Riana Tauro wrote:
>
>
>On 2/8/2025 5:01 AM, Umesh Nerlige Ramappa wrote:
>>On Fri, Feb 07, 2025 at 12:21:24PM +0530, Ghimiray, Himal Prasad wrote:
>>>
>>>
>>>On 07-02-2025 11:48, Riana Tauro wrote:
>>>>
>>>>Hi Himal
>>>>
>>>>On 2/7/2025 8:39 AM, Ghimiray, Himal Prasad wrote:
>>>>>
>>>>>
>>>>>On 06-02-2025 16:13, Riana Tauro wrote:
>>>>>>When the engine events are created, acquire GT forcewake to read gpm
>>>>>>timestamp required for the events and release on event destroy. This
>>>>>>cannot be done during read due to the raw spinlock held my pmu.
>>>>>>
>>>>>>Cc: Rodrigo Vivi <rodrigo.vivi at intel.com>
>>>>>>Cc: Himal Prasad Ghimiray <himal.prasad.ghimiray at intel.com>
>>>>>>Signed-off-by: Riana Tauro <riana.tauro at intel.com>
>>>>>>---
>>>>>> drivers/gpu/drm/xe/xe_pmu.c | 47
>>>>>>++++++++++++++++++++++++++ +++--
>>>>>> drivers/gpu/drm/xe/xe_pmu_types.h | 8 ++++++
>>>>>> 2 files changed, 53 insertions(+), 2 deletions(-)
>>>>>>
>>>>>>diff --git a/drivers/gpu/drm/xe/xe_pmu.c b/drivers/gpu/drm/xe/xe_pmu.c
>>>>>>index 06a1c72a3838..5b5fe4424aba 100644
>>>>>>--- a/drivers/gpu/drm/xe/xe_pmu.c
>>>>>>+++ b/drivers/gpu/drm/xe/xe_pmu.c
>>>>>>@@ -7,6 +7,7 @@
>>>>>> #include <linux/device.h>
>>>>>> #include "xe_device.h"
>>>>>>+#include "xe_force_wake.h"
>>>>>> #include "xe_gt_idle.h"
>>>>>> #include "xe_guc_engine_activity.h"
>>>>>> #include "xe_hw_engine.h"
>>>>>>@@ -102,6 +103,36 @@ static struct xe_hw_engine
>>>>>>*event_to_hwe(struct perf_event *event)
>>>>>> return hwe;
>>>>>> }
>>>>>>+static bool is_engine_event(u64 config)
>>>>>>+{
>>>>>>+ unsigned int event_id = config_to_event_id(config);
>>>>>>+
>>>>>>+ return (event_id == XE_PMU_EVENT_ENGINE_TOTAL_TICKS ||
>>>>>>+ event_id == XE_PMU_EVENT_ENGINE_ACTIVE_TICKS);
>>>>>>+}
>>>>>>+
>>>>>>+static void event_gt_forcewake(struct perf_event *event)
>>>>>>+{
>>>>>>+ struct xe_device *xe = container_of(event->pmu,
>>>>>>typeof(*xe), pmu.base);
>>>>>>+ u64 config = event->attr.config;
>>>>>>+ struct xe_pmu *pmu = &xe->pmu;
>>>>>>+ struct xe_gt *gt;
>>>>>>+ unsigned int fw_ref;
>>>>>>+
>>>>>>+ gt = xe_device_get_gt(xe, config_to_gt_id(config));
>>>>>>+ if (!gt || !is_engine_event(config))
>>>>>>+ return;
>>>>>>+
>>>>>>+ fw_ref = xe_force_wake_get(gt_to_fw(gt), XE_FW_GT);
>>>>>>+ if (!fw_ref)
>>>>>>+ return;
>>>>>>+
>>>>>>+ if (!pmu->fw_ref)
>>>>>>+ pmu->fw_ref = fw_ref;
>>>>>>+
>>>>>>+ pmu->fw_count++;
>>>>>>+}
>>>>>>+
>>>>>> static bool event_supported(struct xe_pmu *pmu, unsigned int gt,
>>>>>> unsigned int id)
>>>>>> {
>>>>>>@@ -144,6 +175,13 @@ static bool event_param_valid(struct
>>>>>>perf_event *event)
>>>>>> static void xe_pmu_event_destroy(struct perf_event *event)
>>>>>> {
>>>>>> struct xe_device *xe = container_of(event->pmu,
>>>>>>typeof(*xe), pmu.base);
>>>>>>+ struct xe_pmu *pmu = &xe->pmu;
>>>>>>+ struct xe_gt *gt;
>>>>>>+
>>>>>>+ if (pmu->fw_count--) {
>>>>>>+ gt = xe_device_get_gt(xe, config_to_gt_id(event-
>>>>>>>attr.config));
>>>>>>+ xe_force_wake_put(gt_to_fw(gt), pmu->fw_ref);
>>>>>>+ }
>>>>>
>>>>>
>>>>>Considering that fw->lock will be acquired and released
>>>>>multiple times during the put operation, this might create an
>>>>>overhead.
>>>>>
>>>>>How about implementing a _put function that can take the
>>>>>number of refcounts to decrement as an input parameter,
>>>>>similar to xe_force_wake_put_many?
>>>>Could you give more details on your suggestion? Would put_many
>>>>just decrement the count? But wouldn't that still require a
>>>>lock? Multiple event_destroys can call the function at the same
>>>>time right?
>>>
>>>I was thinking about putting all refcounts at the end of last
>>>event destroy in case of multiple pmu's.
>>>
>>>>
>>>>
>>>>One thing that can be done is to take forcewake on first count
>>>>and release it when the last event is destroyed in cases of
>>>>multiple
>>>>pmu being used
>>
>>Unless there is a measured inefficiency, I would recommend not
>>refcounting this in PMU. If a forcewake is already taken, the code
>>in forcewake_get is just handling increments and not really
>>accessing MMIO, so we should be okay here.
>>
>>Also, pmu->fw_count is not required, since the force_wake_get logic
>>should be already handling that. We should just call get and put and
>>this should be good enough.
>
>I added the counting because if forcewake get fails then destroy won't
>know if it has to call xe_force_wake_put (multiple perf opened). If
>there is count and ref set, then can be called based on that.
>
>If we can return -ENOTSUPPORTED if forcewake get fails for engine
>events, then the above will work
Hmm, not sure I understand. If forcewake_get fails, then we don't need
to call force_wake_put. Also if force_wake_get fails, we should fail the
event init (which means the destroy should not get called).
Thanks,
Umesh
>
>Thanks
>Riana
>
>>
>>Thanks,
>>Umesh
>>
>>>
>>>This sounds even better.
>>>
>>>>>
>>>>>If the overhead has already been considered and found to be
>>>>>acceptable, I am fine with avoiding unnecessary modifications
>>>>>to this patch.
>>>>This is the first rev for this patch. Open to suggestions
>>>>
>>>>Background for this patch: force_wake is needed to read the timestamp
>>>>register required for engine events.Cannot take it while reading
>>>>the register from pmu_read due to a lockdep splat
>>>>(PROVE_RAW_LOCK_NESTING).
>>>>
>>>>The suggestion was to take forcewake throughout the duration of
>>>>event being read
>>>>
>>>>Thanks
>>>>Riana
>>>>>
>>>>>
>>>>>> drm_WARN_ON(&xe->drm, event->parent);
>>>>>> xe_pm_runtime_put(xe);
>>>>>>@@ -183,18 +221,23 @@ static int xe_pmu_event_init(struct
>>>>>>perf_event *event)
>>>>>> if (!event->parent) {
>>>>>> drm_dev_get(&xe->drm);
>>>>>> xe_pm_runtime_get(xe);
>>>>>>+ event_gt_forcewake(event);
>>>>>> event->destroy = xe_pmu_event_destroy;
>>>>>> }
>>>>>> return 0;
>>>>>> }
>>>>>>-static u64 read_engine_events(struct perf_event *event)
>>>>>>+static u64 read_engine_events(struct perf_event *event, u64 prev)
>>>>>> {
>>>>>> struct xe_device *xe = container_of(event->pmu,
>>>>>>typeof(*xe), pmu.base);
>>>>>>+ struct xe_pmu *pmu = &xe->pmu;
>>>>>> struct xe_hw_engine *hwe;
>>>>>> u64 val = 0;
>>>>>>+ if (!pmu->fw_count)
>>>>>>+ return prev;
>>>>>>+
>>>>>> hwe = event_to_hwe(event);
>>>>>> if (!hwe)
>>>>>> drm_warn(&xe->drm, "unknown pmu engine\n");
>>>>>>@@ -218,7 +261,7 @@ static u64 __xe_pmu_event_read(struct
>>>>>>perf_event *event, u64 prev)
>>>>>> return xe_gt_idle_residency_msec(>->gtidle);
>>>>>> case XE_PMU_EVENT_ENGINE_ACTIVE_TICKS:
>>>>>> case XE_PMU_EVENT_ENGINE_TOTAL_TICKS:
>>>>>>- return read_engine_events(event);
>>>>>>+ return read_engine_events(event, prev);
>>>>>> }
>>>>>> return 0;
>>>>>>diff --git a/drivers/gpu/drm/xe/xe_pmu_types.h
>>>>>>b/drivers/gpu/drm/ xe/ xe_pmu_types.h
>>>>>>index f5ba4d56622c..134b3400b19c 100644
>>>>>>--- a/drivers/gpu/drm/xe/xe_pmu_types.h
>>>>>>+++ b/drivers/gpu/drm/xe/xe_pmu_types.h
>>>>>>@@ -30,6 +30,14 @@ struct xe_pmu {
>>>>>> * @name: Name as registered with perf core.
>>>>>> */
>>>>>> const char *name;
>>>>>>+ /**
>>>>>>+ * @fw_ref: force_wake ref
>>>>>>+ */
>>>>>>+ unsigned int fw_ref;
>>>>>>+ /**
>>>>>>+ * @fw_count: force_wake count
>>>>>>+ */
>>>>>>+ unsigned int fw_count;
>>>>>> /**
>>>>>> * @supported_events: Bitmap of supported events,
>>>>>>indexed by event id
>>>>>> */
>>>>>
>>>>
>>>
>
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