Re: [PATCH v4] accel/rocket: Report NPU usage through fdinfo

["Maíra Canal" <mcanal@igalia.com>]

Hi Tvrtko,

On 05/11/26 06:22, Tvrtko Ursulin wrote:
> 
> On 03/11/2026 15:53, Sidong Yang wrote:
>> There is no way to tell how much of the NPU a client uses. Implement the
>> DRM usage stats: account the time each job occupies a core and report
>> it per client as drm-engine-npu, along with drm_show_memory_stats() for
>> the BOs.
>>
>> The cores are identical, so they are reported as a single engine with
>> drm-engine-capacity-npu set to rdev->max_cores, the number of core
>> slots. The time is summed over all cores, with an atomic counter as the
>> cores complete jobs concurrently.
>>
>> Jobs can outlive the file that submitted them, so the counter is
>> refcounted and each job holds a reference. The time covers the whole
>> period a job owns a core, so it also includes handling the completion
>> interrupt and the gaps between the tasks of a multi-task job.
>>
>> Document the keys in the rocket driver documentation.
>>
>> Signed-off-by: Sidong Yang <sidong.yang@furiosa.ai>
>> ---
>> v4: Report a single drm-engine-npu key with drm-engine-capacity-npu,
>>      instead of drm-engine-npu0..2, as drm-usage-stats.rst specifies for
>>      a group of identical engines, and document the keys (Tomeu Vizoso).
>>      The subject no longer says per-core. Gyeyoung's tags are dropped as
>>      the accounting changed.
>>
>>      Still depends on commit 6eff1d69dae8 ("accel/rocket: search every
>>      core slot when a core is removed") for rdev->max_cores.
>>
>> v3: Add a rocket_engine_usage_create() helper for the counter
>>      allocation in rocket_open(), to pair with
>>      rocket_engine_usage_destroy() (Gyeyoung Baek).
>>
>> v2: Size the per-core counters by rdev->max_cores, the number of core
>>      slots, instead of the number of cores bound when the file is opened.
>>      Sashiko reported the out-of-bounds read and Gyeyoung Baek reproduced
>>      it with KASAN.
>>
>> Link to v3: https://lore.kernel.org/all/20261103104804.1887489-1- 
>> sidong.yang@furiosa.ai/
>> Link to v2: https://lore.kernel.org/all/20261101152723.1430312-1- 
>> sidong.yang@furiosa.ai/
>> Link to v1: https://lore.kernel.org/all/20261031083642.1076356-1- 
>> sidong.yang@furiosa.ai/
>>
>>   Documentation/accel/rocket/index.rst  | 28 +++++++++++
>>   Documentation/gpu/drm-usage-stats.rst |  1 +
>>   drivers/accel/rocket/rocket_drv.c     | 70 ++++++++++++++++++++++++++-
>>   drivers/accel/rocket/rocket_drv.h     | 15 ++++++
>>   drivers/accel/rocket/rocket_job.c     |  7 +++
>>   drivers/accel/rocket/rocket_job.h     |  4 ++
>>   6 files changed, 123 insertions(+), 2 deletions(-)
>>
>> diff --git a/Documentation/accel/rocket/index.rst b/Documentation/ 
>> accel/rocket/index.rst
>> index 70f97bccf100..53c9aa7e2229 100644
>> --- a/Documentation/accel/rocket/index.rst
>> +++ b/Documentation/accel/rocket/index.rst
>> @@ -17,3 +17,31 @@ project.
>>   Hardware currently supported:
>>   * RK3588
>> +
>> +.. _rocket-usage-stats:
>> +
>> +Rocket DRM client usage stats implementation
>> +============================================
>> +
>> +The accel/rocket driver implements the DRM client usage stats 
>> specification as
>> +documented in :ref:`drm-client-usage-stats`.
>> +
>> +The NPU cores are reported as a single engine, npu, with a capacity 
>> equal to the
>> +number of cores. The time is summed over all cores, and covers the 
>> whole period
>> +a job occupies a core.
>> +
>> +Example of the output showing the implemented key value pairs:
>> +
>> +::
>> +
>> +        pos:    0
>> +        flags:    02400002
>> +        mnt_id:    33
>> +        ino:    749
>> +        drm-driver:    rocket
>> +        drm-client-id:    246
>> +        drm-engine-npu:    2296549300 ns
>> +        drm-engine-capacity-npu:    3
>> +        drm-total-memory:    24216 KiB
>> +        drm-shared-memory:    0
>> +        drm-active-memory:    1920 KiB
>> diff --git a/Documentation/gpu/drm-usage-stats.rst b/Documentation/ 
>> gpu/drm-usage-stats.rst
>> index 70b7cfcc194f..288764730d23 100644
>> --- a/Documentation/gpu/drm-usage-stats.rst
>> +++ b/Documentation/gpu/drm-usage-stats.rst
>> @@ -218,3 +218,4 @@ Driver specific implementations
>>   * :ref:`panthor-usage-stats`
>>   * :ref:`xe-usage-stats`
>>   * :ref:`amdxdna-usage-stats`
>> +* :ref:`rocket-usage-stats`
>> diff --git a/drivers/accel/rocket/rocket_drv.c b/drivers/accel/rocket/ 
>> rocket_drv.c
>> index 2bcfe4ab3c68..e22e8623db64 100644
>> --- a/drivers/accel/rocket/rocket_drv.c
>> +++ b/drivers/accel/rocket/rocket_drv.c
>> @@ -3,8 +3,10 @@
>>   #include <drm/drm_accel.h>
>>   #include <drm/drm_drv.h>
>> +#include <drm/drm_file.h>
>>   #include <drm/drm_gem.h>
>>   #include <drm/drm_ioctl.h>
>> +#include <drm/drm_print.h>
>>   #include <drm/rocket_accel.h>
>>   #include <linux/clk.h>
>>   #include <linux/err.h>
>> @@ -68,6 +70,38 @@ rocket_iommu_domain_put(struct rocket_iommu_domain 
>> *domain)
>>       kref_put(&domain->kref, rocket_iommu_domain_destroy);
>>   }
>> +static struct rocket_engine_usage *
>> +rocket_engine_usage_create(void)
>> +{
>> +    struct rocket_engine_usage *usage;
>> +
>> +    usage = kzalloc_obj(*usage);
>> +    if (!usage)
>> +        return NULL;
>> +    kref_init(&usage->kref);
>> +
>> +    return usage;
>> +}
>> +
>> +static void
>> +rocket_engine_usage_destroy(struct kref *kref)
>> +{
>> +    kfree(container_of(kref, struct rocket_engine_usage, kref));
>> +}
>> +
>> +struct rocket_engine_usage *
>> +rocket_engine_usage_get(struct rocket_file_priv *rocket_priv)
>> +{
>> +    kref_get(&rocket_priv->engine_usage->kref);
>> +    return rocket_priv->engine_usage;
>> +}
>> +
>> +void
>> +rocket_engine_usage_put(struct rocket_engine_usage *usage)
>> +{
>> +    kref_put(&usage->kref, rocket_engine_usage_destroy);
>> +}
>> +
>>   static int
>>   rocket_open(struct drm_device *dev, struct drm_file *file)
>>   {
>> @@ -86,10 +120,17 @@ rocket_open(struct drm_device *dev, struct 
>> drm_file *file)
>>       }
>>       rocket_priv->rdev = rdev;
>> +
>> +    rocket_priv->engine_usage = rocket_engine_usage_create();
>> +    if (!rocket_priv->engine_usage) {
>> +        ret = -ENOMEM;
>> +        goto err_free;
>> +    }
> 
> Glanced over this patch by chance and it very reminded me of 
> drm_sched_entity_stats tracking. That object is reference counted by the 
> entity so I think it would satisfy your requirements. We would only need 
> to add an accessor like drm_sched_entity_get_runtime() and just call it 
> from rocket. Thoughts?
> 

I believe we tried something similar in the past (commit 97804a133c68)
and it ended up being reverted after this regression [1]. I would be
great to give this idea another change (specially now that we have
drm_sched_entity_stats), as it would also be useful for V3D.

[1] 
https://lore.kernel.org/dri-devel/3e00d8a9-b6c4-8202-4f2d-5a659c61d094@redhat.com/

Best regards,
- Maíra