Message-ID: <c73ad42b-a8db-23c2-86c7-1a2939dba044@linux.intel.com>
Date:   Mon, 25 Sep 2023 09:57:50 +0100
From:   Tvrtko Ursulin <tvrtko.ursulin@...ux.intel.com>
To:     Steven Price <steven.price@....com>,
        Adrián Larumbe <adrian.larumbe@...labora.com>
Cc:     maarten.lankhorst@...ux.intel.com, mripard@...nel.org,
        tzimmermann@...e.de, airlied@...il.com, daniel@...ll.ch,
        robdclark@...il.com, quic_abhinavk@...cinc.com,
        dmitry.baryshkov@...aro.org, sean@...rly.run,
        marijn.suijten@...ainline.org, robh@...nel.org,
        linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, healych@...zon.com,
        Boris Brezillon <boris.brezillon@...labora.com>,
        kernel@...labora.com, freedreno@...ts.freedesktop.org
Subject: Re: [PATCH v6 2/6] drm/panfrost: Add fdinfo support GPU load metrics


On 22/09/2023 16:23, Steven Price wrote:
> On 22/09/2023 14:53, Tvrtko Ursulin wrote:
>>
>> On 22/09/2023 11:57, Adrián Larumbe wrote:
>>> On 20.09.2023 16:40, Tvrtko Ursulin wrote:
>>>> On 20/09/2023 00:34, Adrián Larumbe wrote:
>>>>> The drm-stats fdinfo tags made available to user space are drm-engine,
>>>>> drm-cycles, drm-max-freq and drm-curfreq, one per job slot.
>>>>>
>>>>> This deviates from standard practice in other DRM drivers, where a
>>>>> single
>>>>> set of key:value pairs is provided for the whole render engine.
>>>>> However,
>>>>> Panfrost has separate queues for fragment and vertex/tiler jobs, so a
>>>>> decision was made to calculate bus cycles and workload times
>>>>> separately.
>>>>>
>>>>> Maximum operating frequency is calculated at devfreq initialisation
>>>>> time.
>>>>> Current frequency is made available to user space because nvtop uses it
>>>>> when performing engine usage calculations.
>>>>>
>>>>> It is important to bear in mind that both GPU cycle and kernel time
>>>>> numbers
>>>>> provided are at best rough estimations, and always reported in
>>>>> excess from
>>>>> the actual figure because of two reasons:
>>>>>     - Excess time because of the delay between the end of a job
>>>>> processing,
>>>>>       the subsequent job IRQ and the actual time of the sample.
>>>>>     - Time spent in the engine queue waiting for the GPU to pick up
>>>>> the next
>>>>>       job.
>>>>>
>>>>> To avoid race conditions during enablement/disabling, a reference
>>>>> counting
>>>>> mechanism was introduced, and a job flag that tells us whether a
>>>>> given job
>>>>> increased the refcount. This is necessary, because user space can
>>>>> toggle
>>>>> cycle counting through a debugfs file, and a given job might have
>>>>> been in
>>>>> flight by the time cycle counting was disabled.
>>>>>
>>>>> The main goal of the debugfs cycle counter knob is letting tools
>>>>> like nvtop
>>>>> or IGT's gputop switch it at any time, to avoid power waste in case no
>>>>> engine usage measuring is necessary.
>>>>>
>>>>> Signed-off-by: Adrián Larumbe <adrian.larumbe@...labora.com>
>>>>> Reviewed-by: Boris Brezillon <boris.brezillon@...labora.com>
>>>>> Reviewed-by: Steven Price <steven.price@....com>
>>>>> ---
>>>>>     drivers/gpu/drm/panfrost/Makefile           |  2 +
>>>>>     drivers/gpu/drm/panfrost/panfrost_debugfs.c | 20 ++++++++
>>>>>     drivers/gpu/drm/panfrost/panfrost_debugfs.h | 13 +++++
>>>>>     drivers/gpu/drm/panfrost/panfrost_devfreq.c |  8 +++
>>>>>     drivers/gpu/drm/panfrost/panfrost_devfreq.h |  3 ++
>>>>>     drivers/gpu/drm/panfrost/panfrost_device.c  |  2 +
>>>>>     drivers/gpu/drm/panfrost/panfrost_device.h  | 13 +++++
>>>>>     drivers/gpu/drm/panfrost/panfrost_drv.c     | 57
>>>>> ++++++++++++++++++++-
>>>>>     drivers/gpu/drm/panfrost/panfrost_gpu.c     | 41 +++++++++++++++
>>>>>     drivers/gpu/drm/panfrost/panfrost_gpu.h     |  4 ++
>>>>>     drivers/gpu/drm/panfrost/panfrost_job.c     | 24 +++++++++
>>>>>     drivers/gpu/drm/panfrost/panfrost_job.h     |  5 ++
>>>>>     12 files changed, 191 insertions(+), 1 deletion(-)
>>>>>     create mode 100644 drivers/gpu/drm/panfrost/panfrost_debugfs.c
>>>>>     create mode 100644 drivers/gpu/drm/panfrost/panfrost_debugfs.h
>>>>>
>>>>> diff --git a/drivers/gpu/drm/panfrost/Makefile
>>>>> b/drivers/gpu/drm/panfrost/Makefile
>>>>> index 7da2b3f02ed9..2c01c1e7523e 100644
>>>>> --- a/drivers/gpu/drm/panfrost/Makefile
>>>>> +++ b/drivers/gpu/drm/panfrost/Makefile
>>>>> @@ -12,4 +12,6 @@ panfrost-y := \
>>>>>         panfrost_perfcnt.o \
>>>>>         panfrost_dump.o
>>>>> +panfrost-$(CONFIG_DEBUG_FS) += panfrost_debugfs.o
>>>>> +
>>>>>     obj-$(CONFIG_DRM_PANFROST) += panfrost.o
>>>>> diff --git a/drivers/gpu/drm/panfrost/panfrost_debugfs.c
>>>>> b/drivers/gpu/drm/panfrost/panfrost_debugfs.c
>>>>> new file mode 100644
>>>>> index 000000000000..cc14eccba206
>>>>> --- /dev/null
>>>>> +++ b/drivers/gpu/drm/panfrost/panfrost_debugfs.c
>>>>> @@ -0,0 +1,20 @@
>>>>> +// SPDX-License-Identifier: GPL-2.0
>>>>> +/* Copyright 2023 Collabora ltd. */
>>>>> +
>>>>> +#include <linux/debugfs.h>
>>>>> +#include <linux/platform_device.h>
>>>>> +#include <drm/drm_debugfs.h>
>>>>> +#include <drm/drm_file.h>
>>>>> +#include <drm/panfrost_drm.h>
>>>>> +
>>>>> +#include "panfrost_device.h"
>>>>> +#include "panfrost_gpu.h"
>>>>> +#include "panfrost_debugfs.h"
>>>>> +
>>>>> +void panfrost_debugfs_init(struct drm_minor *minor)
>>>>> +{
>>>>> +    struct drm_device *dev = minor->dev;
>>>>> +    struct panfrost_device *pfdev =
>>>>> platform_get_drvdata(to_platform_device(dev->dev));
>>>>> +
>>>>> +    debugfs_create_atomic_t("profile", 0600, minor->debugfs_root,
>>>>> &pfdev->profile_mode);
>>>>> +}
>>>>> diff --git a/drivers/gpu/drm/panfrost/panfrost_debugfs.h
>>>>> b/drivers/gpu/drm/panfrost/panfrost_debugfs.h
>>>>> new file mode 100644
>>>>> index 000000000000..db1c158bcf2f
>>>>> --- /dev/null
>>>>> +++ b/drivers/gpu/drm/panfrost/panfrost_debugfs.h
>>>>> @@ -0,0 +1,13 @@
>>>>> +/* SPDX-License-Identifier: GPL-2.0 */
>>>>> +/*
>>>>> + * Copyright 2023 Collabora ltd.
>>>>> + */
>>>>> +
>>>>> +#ifndef PANFROST_DEBUGFS_H
>>>>> +#define PANFROST_DEBUGFS_H
>>>>> +
>>>>> +#ifdef CONFIG_DEBUG_FS
>>>>> +void panfrost_debugfs_init(struct drm_minor *minor);
>>>>> +#endif
>>>>> +
>>>>> +#endif  /* PANFROST_DEBUGFS_H */
>>>>> diff --git a/drivers/gpu/drm/panfrost/panfrost_devfreq.c
>>>>> b/drivers/gpu/drm/panfrost/panfrost_devfreq.c
>>>>> index 58dfb15a8757..28caffc689e2 100644
>>>>> --- a/drivers/gpu/drm/panfrost/panfrost_devfreq.c
>>>>> +++ b/drivers/gpu/drm/panfrost/panfrost_devfreq.c
>>>>> @@ -58,6 +58,7 @@ static int panfrost_devfreq_get_dev_status(struct
>>>>> device *dev,
>>>>>         spin_lock_irqsave(&pfdevfreq->lock, irqflags);
>>>>>         panfrost_devfreq_update_utilization(pfdevfreq);
>>>>> +    pfdevfreq->current_frequency = status->current_frequency;
>>>>>         status->total_time = ktime_to_ns(ktime_add(pfdevfreq->busy_time,
>>>>>                                pfdevfreq->idle_time));
>>>>> @@ -117,6 +118,7 @@ int panfrost_devfreq_init(struct panfrost_device
>>>>> *pfdev)
>>>>>         struct devfreq *devfreq;
>>>>>         struct thermal_cooling_device *cooling;
>>>>>         struct panfrost_devfreq *pfdevfreq = &pfdev->pfdevfreq;
>>>>> +    unsigned long freq = ULONG_MAX;
>>>>>         if (pfdev->comp->num_supplies > 1) {
>>>>>             /*
>>>>> @@ -172,6 +174,12 @@ int panfrost_devfreq_init(struct
>>>>> panfrost_device *pfdev)
>>>>>             return ret;
>>>>>         }
>>>>> +    /* Find the fastest defined rate  */
>>>>> +    opp = dev_pm_opp_find_freq_floor(dev, &freq);
>>>>> +    if (IS_ERR(opp))
>>>>> +        return PTR_ERR(opp);
>>>>> +    pfdevfreq->fast_rate = freq;
>>>>> +
>>>>>         dev_pm_opp_put(opp);
>>>>>         /*
>>>>> diff --git a/drivers/gpu/drm/panfrost/panfrost_devfreq.h
>>>>> b/drivers/gpu/drm/panfrost/panfrost_devfreq.h
>>>>> index 1514c1f9d91c..48dbe185f206 100644
>>>>> --- a/drivers/gpu/drm/panfrost/panfrost_devfreq.h
>>>>> +++ b/drivers/gpu/drm/panfrost/panfrost_devfreq.h
>>>>> @@ -19,6 +19,9 @@ struct panfrost_devfreq {
>>>>>         struct devfreq_simple_ondemand_data gov_data;
>>>>>         bool opp_of_table_added;
>>>>> +    unsigned long current_frequency;
>>>>> +    unsigned long fast_rate;
>>>>> +
>>>>>         ktime_t busy_time;
>>>>>         ktime_t idle_time;
>>>>>         ktime_t time_last_update;
>>>>> diff --git a/drivers/gpu/drm/panfrost/panfrost_device.c
>>>>> b/drivers/gpu/drm/panfrost/panfrost_device.c
>>>>> index fa1a086a862b..28f7046e1b1a 100644
>>>>> --- a/drivers/gpu/drm/panfrost/panfrost_device.c
>>>>> +++ b/drivers/gpu/drm/panfrost/panfrost_device.c
>>>>> @@ -207,6 +207,8 @@ int panfrost_device_init(struct panfrost_device
>>>>> *pfdev)
>>>>>         spin_lock_init(&pfdev->as_lock);
>>>>> +    spin_lock_init(&pfdev->cycle_counter.lock);
>>>>> +
>>>>>         err = panfrost_clk_init(pfdev);
>>>>>         if (err) {
>>>>>             dev_err(pfdev->dev, "clk init failed %d\n", err);
>>>>> diff --git a/drivers/gpu/drm/panfrost/panfrost_device.h
>>>>> b/drivers/gpu/drm/panfrost/panfrost_device.h
>>>>> index b0126b9fbadc..1e85656dc2f7 100644
>>>>> --- a/drivers/gpu/drm/panfrost/panfrost_device.h
>>>>> +++ b/drivers/gpu/drm/panfrost/panfrost_device.h
>>>>> @@ -107,6 +107,7 @@ struct panfrost_device {
>>>>>         struct list_head scheduled_jobs;
>>>>>         struct panfrost_perfcnt *perfcnt;
>>>>> +    atomic_t profile_mode;
>>>>>         struct mutex sched_lock;
>>>>> @@ -121,6 +122,11 @@ struct panfrost_device {
>>>>>         struct shrinker shrinker;
>>>>>         struct panfrost_devfreq pfdevfreq;
>>>>> +
>>>>> +    struct {
>>>>> +        atomic_t use_count;
>>>>> +        spinlock_t lock;
>>>>> +    } cycle_counter;
>>>>>     };
>>>>>     struct panfrost_mmu {
>>>>> @@ -135,12 +141,19 @@ struct panfrost_mmu {
>>>>>         struct list_head list;
>>>>>     };
>>>>> +struct panfrost_engine_usage {
>>>>> +    unsigned long long elapsed_ns[NUM_JOB_SLOTS];
>>>>> +    unsigned long long cycles[NUM_JOB_SLOTS];
>>>>> +};
>>>>> +
>>>>>     struct panfrost_file_priv {
>>>>>         struct panfrost_device *pfdev;
>>>>>         struct drm_sched_entity sched_entity[NUM_JOB_SLOTS];
>>>>>         struct panfrost_mmu *mmu;
>>>>> +
>>>>> +    struct panfrost_engine_usage engine_usage;
>>>>>     };
>>>>>     static inline struct panfrost_device *to_panfrost_device(struct
>>>>> drm_device *ddev)
>>>>> diff --git a/drivers/gpu/drm/panfrost/panfrost_drv.c
>>>>> b/drivers/gpu/drm/panfrost/panfrost_drv.c
>>>>> index a2ab99698ca8..3c93a11deab1 100644
>>>>> --- a/drivers/gpu/drm/panfrost/panfrost_drv.c
>>>>> +++ b/drivers/gpu/drm/panfrost/panfrost_drv.c
>>>>> @@ -20,6 +20,7 @@
>>>>>     #include "panfrost_job.h"
>>>>>     #include "panfrost_gpu.h"
>>>>>     #include "panfrost_perfcnt.h"
>>>>> +#include "panfrost_debugfs.h"
>>>>>     static bool unstable_ioctls;
>>>>>     module_param_unsafe(unstable_ioctls, bool, 0600);
>>>>> @@ -267,6 +268,7 @@ static int panfrost_ioctl_submit(struct
>>>>> drm_device *dev, void *data,
>>>>>         job->requirements = args->requirements;
>>>>>         job->flush_id = panfrost_gpu_get_latest_flush_id(pfdev);
>>>>>         job->mmu = file_priv->mmu;
>>>>> +    job->engine_usage = &file_priv->engine_usage;
>>>>>         slot = panfrost_job_get_slot(job);
>>>>> @@ -523,7 +525,55 @@ static const struct drm_ioctl_desc
>>>>> panfrost_drm_driver_ioctls[] = {
>>>>>         PANFROST_IOCTL(MADVISE,        madvise,    DRM_RENDER_ALLOW),
>>>>>     };
>>>>> -DEFINE_DRM_GEM_FOPS(panfrost_drm_driver_fops);
>>>>> +
>>>>> +static void panfrost_gpu_show_fdinfo(struct panfrost_device *pfdev,
>>>>> +                     struct panfrost_file_priv *panfrost_priv,
>>>>> +                     struct drm_printer *p)
>>>>> +{
>>>>> +    int i;
>>>>> +
>>>>> +    /*
>>>>> +     * IMPORTANT NOTE: drm-cycles and drm-engine measurements are not
>>>>> +     * accurate, as they only provide a rough estimation of the
>>>>> number of
>>>>> +     * GPU cycles and CPU time spent in a given context. This is
>>>>> due to two
>>>>> +     * different factors:
>>>>> +     * - Firstly, we must consider the time the CPU and then the
>>>>> kernel
>>>>> +     *   takes to process the GPU interrupt, which means additional
>>>>> time and
>>>>> +     *   GPU cycles will be added in excess to the real figure.
>>>>> +     * - Secondly, the pipelining done by the Job Manager (2 job
>>>>> slots per
>>>>> +     *   engine) implies there is no way to know exactly how much
>>>>> time each
>>>>> +     *   job spent on the GPU.
>>>>> +     */
>>>>> +
>>>>> +    static const char * const engine_names[] = {
>>>>> +        "fragment", "vertex-tiler", "compute-only"
>>>>> +    };
>>>>> +
>>>>> +    for (i = 0; i < NUM_JOB_SLOTS - 1; i++) {
>>>>
>>>> FWIW you could future proof this a bit by using "i <
>>>> ARRAY_SIZE(engine_names)"
>>>> and avoid maybe silent out of bounds reads if someone updates
>>>> NUM_JOB_SLOTS
>>>> and forgets about this loop. Or stick a warning of some sort.
>>>>
>>> NUM_JOB_SLOTS is actually the same as the number of engines in the
>>> device. I decided to follow
>>> this loop convention because that's what's being done across the
>>> driver when manipulating
>>> the engine queues, so I thought I'd stick to it for the sake of
>>> consistency. Bear in mind
>>> the loop doesn't pick up the compute-only engine because it's still
>>> not exposed to user space.
>>>
>>> So NUM_JOB_SLOTS cannot change, unless a new engine were introduced,
>>> and then someone would
>>> have to update this array accordingly.
>>
>> Exactly, and until they would, here we'd have a be silent out of bound
>> memory access. Content of which even gets shared with userspace. ;)
> 
> I think using NUM_JOB_SLOTS here seems sensible (as Adrián points out
> it's consistent with the rest of the driver). But a BUILD_BUG_ON
> checking the array size is could make sense.
> 
> In reality I don't see the number of job slots ever changing - panfrost
> is now for the 'old' architecture (panthor being the new driver for
> later 'CSF' architecture). And even if there was a new design for
> pre-CSF - it would be a very big change to the architecture: we've kept
> the 3 slots all the way through even though the 3rd is never used on
> most GPUs. But equally I've been wrong before ;)

Thanks for this explanation - with that it indeed isn't much need to 
robustify it.

Regards,

Tvrtko

> 
> Steve
> 
>>>>> +        drm_printf(p, "drm-engine-%s:\t%llu ns\n",
>>>>> +               engine_names[i],
>>>>> panfrost_priv->engine_usage.elapsed_ns[i]);
>>>>> +        drm_printf(p, "drm-cycles-%s:\t%llu\n",
>>>>> +               engine_names[i],
>>>>> panfrost_priv->engine_usage.cycles[i]);
>>>>> +        drm_printf(p, "drm-maxfreq-%s:\t%lu Hz\n",
>>>>> +               engine_names[i], pfdev->pfdevfreq.fast_rate);
>>>>> +        drm_printf(p, "drm-curfreq-%s:\t%lu Hz\n",
>>>>> +               engine_names[i], pfdev->pfdevfreq.current_frequency);
>>>>
>>>> I envisaged a link to driver specific docs at the bottom of
>>>> drm-usage-stats.rst so it would be nice if drivers would be adding those
>>>> sections and describing their private keys, engine names etc. ;)
>>>>
>>> Currently there's no panfrost.rst file under Documentation/gpu. I
>>> guess I'll create a new
>>> one and add the engine descriptions and meaning of drm-curfreq key.
>>
>> Yeah I have to do the same for i915 in my memory stats series. :)
>>
>> Regards,
>>
>> Tvrtko
> 

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