Re: [PATCH v5 5/8] drm/xe/xe_pmu: Acquire forcewake on event init for engine events

[Riana Tauro <riana.tauro@intel.com>]

On 2/11/2025 11:03 PM, Umesh Nerlige Ramappa wrote:
> 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@intel.com>
>>>>>>> Cc: Himal Prasad Ghimiray <himal.prasad.ghimiray@intel.com>
>>>>>>> Signed-off-by: Riana Tauro <riana.tauro@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).

Yeah this is what i meant, since force_wake needs runtime pm.
Have done the above in v6

Thanks
Riana
> 
> 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(&gt->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
>>>>>>>        */
>>>>>>
>>>>>
>>>>
>>