On 08/07/2026 04:24, Guangliu Ding wrote:
> Expose GPU utilization via /sys/kernel/debug/dri/<N>/gpu_load. The
> file reports busy_time_ns, idle_time_ns and gpu_load %.
>
> Values are snapshotted at the end of each devfreq sampling window
> (~50 ms) rather than read from live accumulators, avoiding load swings
> over short observation intervals.
>
> The snapshot is cleared on suspend to avoid stale data when the GPU
> is powered off.
>
> Signed-off-by: Guangliu Ding <[email protected]>
Hi Guangliu,
I'm puzzled exactly what you're trying to achieve with this. I can see
that getting the GPU load might be useful, we do already have the
'fdinfo' mechanism to do this in a per-client manner but nothing good
for "whole GPU" measurements.
But stashing it in debugfs and formatting it as a string seems odd. Do
you have a tool which uses this file, or is just for 'cat'ing to see the
instantaneous load?
Ideally we'd have something that would provide this information in a
format that all drivers could implement, and not rely on debugfs files.
Thanks,
Steve
> ---
> Add /sys/kernel/debug/dri/<N>/gpu_load to expose GPU utilisation
> from the last devfreq sampling window (~50 ms).
> The file reports busy_time_ns, idle_time_ns and load percentage.
>
> Tested on NXP i.MX95 EVK (Mali-G310 V2).
> ---
> drivers/gpu/drm/panthor/panthor_devfreq.c | 80
> +++++++++++++++++++++++++++++++
> drivers/gpu/drm/panthor/panthor_devfreq.h | 6 +++
> drivers/gpu/drm/panthor/panthor_drv.c | 2 +
> 3 files changed, 88 insertions(+)
>
> diff --git a/drivers/gpu/drm/panthor/panthor_devfreq.c
> b/drivers/gpu/drm/panthor/panthor_devfreq.c
> index 2249b41ca4af..1b3f58ddfbd3 100644
> --- a/drivers/gpu/drm/panthor/panthor_devfreq.c
> +++ b/drivers/gpu/drm/panthor/panthor_devfreq.c
> @@ -1,12 +1,16 @@
> // SPDX-License-Identifier: GPL-2.0 or MIT
> /* Copyright 2019 Collabora ltd. */
> +/* Copyright 2026 NXP */
>
> #include <linux/clk.h>
> +#include <linux/debugfs.h>
> #include <linux/devfreq.h>
> #include <linux/devfreq_cooling.h>
> +#include <linux/math64.h>
> #include <linux/platform_device.h>
> #include <linux/pm_opp.h>
>
> +#include <drm/drm_file.h>
> #include <drm/drm_managed.h>
> #include <drm/drm_print.h>
>
> @@ -43,6 +47,22 @@ struct panthor_devfreq {
> * and panthor_devfreq_record_{busy,idle}().
> */
> spinlock_t lock;
> +
> +#ifdef CONFIG_DEBUG_FS
> + /**
> + * @last_busy_ns: Busy time in nanoseconds of the last completed
> devfreq window.
> + * Updated by panthor_devfreq_get_dev_status() before resetting the
> counters.
> + * Protected by @lock.
> + */
> + u64 last_busy_ns;
> +
> + /**
> + * @last_total_ns: Total time in nanoseconds of the last completed
> devfreq window.
> + * Updated by panthor_devfreq_get_dev_status() before resetting the
> counters.
> + * Protected by @lock.
> + */
> + u64 last_total_ns;
> +#endif
> };
>
> static void panthor_devfreq_update_utilization(struct panthor_devfreq
> *pdevfreq)
> @@ -101,6 +121,11 @@ static int panthor_devfreq_get_dev_status(struct device
> *dev,
>
> status->busy_time = ktime_to_ns(pdevfreq->busy_time);
>
> +#ifdef CONFIG_DEBUG_FS
> + pdevfreq->last_busy_ns = status->busy_time;
> + pdevfreq->last_total_ns = status->total_time;
> +#endif
> +
> panthor_devfreq_reset(pdevfreq);
>
> spin_unlock_irqrestore(&pdevfreq->lock, irqflags);
> @@ -283,6 +308,17 @@ void panthor_devfreq_suspend(struct panthor_device
> *ptdev)
> return;
>
> drm_WARN_ON(&ptdev->base, devfreq_suspend_device(pdevfreq->devfreq));
> +
> +#ifdef CONFIG_DEBUG_FS
> + {
> + unsigned long irqflags;
> +
> + spin_lock_irqsave(&pdevfreq->lock, irqflags);
> + pdevfreq->last_busy_ns = 0;
> + pdevfreq->last_total_ns = 0;
> + spin_unlock_irqrestore(&pdevfreq->lock, irqflags);
> + }
> +#endif
> }
>
> void panthor_devfreq_record_busy(struct panthor_device *ptdev)
> @@ -332,3 +368,47 @@ unsigned long panthor_devfreq_get_freq(struct
> panthor_device *ptdev)
>
> return freq;
> }
> +
> +#ifdef CONFIG_DEBUG_FS
> +static int panthor_devfreq_gpu_load_show(struct seq_file *m, void *unused)
> +{
> + struct panthor_device *ptdev = m->private;
> + struct panthor_devfreq *pdevfreq = ptdev->devfreq;
> + unsigned long irqflags;
> + unsigned int gpu_load;
> + u64 total_ns;
> + u64 busy_ns;
> +
> + if (!pdevfreq->devfreq) {
> + seq_puts(m, "devfreq not initialized\n");
> + return 0;
> + }
> +
> + spin_lock_irqsave(&pdevfreq->lock, irqflags);
> + busy_ns = pdevfreq->last_busy_ns;
> + total_ns = pdevfreq->last_total_ns;
> + spin_unlock_irqrestore(&pdevfreq->lock, irqflags);
> +
> + busy_ns = min(busy_ns, total_ns);
> + gpu_load = total_ns ? (unsigned int)div64_u64(busy_ns * 100ULL,
> total_ns) : 0;
> +
> + seq_printf(m, "busy_time_ns: %llu idle_time_ns: %llu gpu_load:
> %u%%\n",
> + busy_ns, total_ns - busy_ns, gpu_load);
> +
> + return 0;
> +}
> +DEFINE_SHOW_ATTRIBUTE(panthor_devfreq_gpu_load);
> +
> +/**
> + * panthor_devfreq_debugfs_init() - Initialize devfreq debugfs entries
> + * @minor: DRM minor.
> + */
> +void panthor_devfreq_debugfs_init(struct drm_minor *minor)
> +{
> + struct panthor_device *ptdev = container_of(minor->dev,
> + struct panthor_device,
> base);
> +
> + debugfs_create_file("gpu_load", 0444, minor->debugfs_root, ptdev,
> + &panthor_devfreq_gpu_load_fops);
> +}
> +#endif /* CONFIG_DEBUG_FS */
> diff --git a/drivers/gpu/drm/panthor/panthor_devfreq.h
> b/drivers/gpu/drm/panthor/panthor_devfreq.h
> index f8e29e02f66c..4552569abfe4 100644
> --- a/drivers/gpu/drm/panthor/panthor_devfreq.h
> +++ b/drivers/gpu/drm/panthor/panthor_devfreq.h
> @@ -1,5 +1,6 @@
> /* SPDX-License-Identifier: GPL-2.0 or MIT */
> /* Copyright 2019 Collabora ltd. */
> +/* Copyright 2026 NXP */
>
> #ifndef __PANTHOR_DEVFREQ_H__
> #define __PANTHOR_DEVFREQ_H__
> @@ -20,4 +21,9 @@ void panthor_devfreq_record_idle(struct panthor_device
> *ptdev);
>
> unsigned long panthor_devfreq_get_freq(struct panthor_device *ptdev);
>
> +#ifdef CONFIG_DEBUG_FS
> +struct drm_minor;
> +void panthor_devfreq_debugfs_init(struct drm_minor *minor);
> +#endif
> +
> #endif /* __PANTHOR_DEVFREQ_H__ */
> diff --git a/drivers/gpu/drm/panthor/panthor_drv.c
> b/drivers/gpu/drm/panthor/panthor_drv.c
> index e8dc4096c1d2..4093a6d21337 100644
> --- a/drivers/gpu/drm/panthor/panthor_drv.c
> +++ b/drivers/gpu/drm/panthor/panthor_drv.c
> @@ -2,6 +2,7 @@
> /* Copyright 2018 Marty E. Plummer <[email protected]> */
> /* Copyright 2019 Linaro, Ltd., Rob Herring <[email protected]> */
> /* Copyright 2019 Collabora ltd. */
> +/* Copyright 2026 NXP */
>
> #ifdef CONFIG_ARM_ARCH_TIMER
> #include <asm/arch_timer.h>
> @@ -1761,6 +1762,7 @@ static void panthor_debugfs_init(struct drm_minor
> *minor)
> {
> panthor_mmu_debugfs_init(minor);
> panthor_gem_debugfs_init(minor);
> + panthor_devfreq_debugfs_init(minor);
> }
> #endif
>
>
> ---
> base-commit: 8cdeaa50eae8dad34885515f62559ee83e7e8dda
> change-id: 20260706-master-bd0eef99ca8e
>
> Best regards,
> --
> Guangliu Ding <[email protected]>
>
