> On 13/07/2026 04:19, Guangliu Ding wrote:
> >> 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
> >>
> >
> > Hi Steve
> >
> > Panthor currently exposes very limited runtime telemetry. The intent
> > is to expose utilization in this patch, together with other
> > device-wide GPU runtime metrics (frequency, shader activity, draw-call
> > counts,
> memory usage, etc.) to a userspace tool for monitoring and
> workload-optimization purposes.
> >
> > fdinfo is primarily a per-client interface. Since it requires an open
> > DRM fd and reports information associated with that client, it does
> > not map particularly well to the global metrics exported by this patch.
> >
> > If a generic cross-driver interface for this kind of GPU telemetry
> > emerges, I'm happy to switch to it. However, no such interface
> > currently exists for devfreq-based device utilization, so debugfs
> > seemed like the most appropriate existing option. Suggestions for a better
> interface are welcome.
>
> So my point really is someone should ideally implement a better interface that
> multiple drivers can use. Having a point hack for one driver doesn't really
> help
> the situation.
>
> Indeed you can get the load information with ftrace already:
>
> cd /sys/kernel/tracing
> echo 0 > tracing_on
> echo > trace
> echo 'dev_name == "fb000000.gpu"' > events/devfreq/devfreq_monitor/filter
> echo 1 > events/devfreq/devfreq_monitor/enable
> echo 1 > tracing_on
> cat trace_pipe
>
> And you'll get a stream of messages when the GPU is in use which includes a
> "load=xx" value at the end.
>
> If this is going to be extended to other properties for a user space tool
> then we
> should probably be putting this in sysfs and trying to come up with a design
> that
> other drivers can copy.
>
> Thanks,
> Steve
>
Hi Steve,
Thanks for the feedback and sharing.
I agree that a generic interface shared by multiple drivers would be preferable
in the long term.
For our use case, we need to provide customers with a simple way to quickly
observe GPU
performance metrics from a userspace tuning tool. Even though the
devfreq_monitor tracepoint already
exposes the load information, ftrace is typically not enabled or supported in
our deployed products,
making it unsuitable as a user-facing interface for the tool.
As far as I know, there is currently no generic DRM/devfreq interface for
querying device-wide
GPU utilization on demand. Given that gap, exporting the information through
debugfs
seemed like the most practical option for Panthor today.
Thanks,
Guangliu
> > Best Regards,
> > Guangliu
> >
> >>> ---
> >>> 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]>
> >>>
> >
