Re: [PATCH 2/4] drm/etnaviv: add loadavg accounting

Hoi Lucas,

Am Fr., 10. Juli 2020 um 10:19 Uhr schrieb Lucas Stach l.stach@pengutronix.de:

Hi Christian,

Am Freitag, den 10.07.2020, 09:41 +0200 schrieb Christian Gmeiner:

...

The GPU has an idle state register where each bit represents the idle state of a sub-GPU component like FE or TX. Sample this register every 10ms and calculate a simple moving average over the sub-GPU component idle states with a total observation time frame of 1s.

This provides us with a percentage based load of each sub-GPU component.

Signed-off-by: Christian Gmeiner christian.gmeiner@gmail.com

drivers/gpu/drm/etnaviv/etnaviv_drv.c | 14 ++++++++++++ drivers/gpu/drm/etnaviv/etnaviv_gpu.c | 32 +++++++++++++++++++++++++++ drivers/gpu/drm/etnaviv/etnaviv_gpu.h | 29 ++++++++++++++++++++++++ 3 files changed, 75 insertions(+)

diff --git a/drivers/gpu/drm/etnaviv/etnaviv_drv.c b/drivers/gpu/drm/etnaviv/etnaviv_drv.c index f9afe11c50f0..b31920241c86 100644 --- a/drivers/gpu/drm/etnaviv/etnaviv_drv.c +++ b/drivers/gpu/drm/etnaviv/etnaviv_drv.c @@ -46,6 +46,19 @@ static void load_gpu(struct drm_device *dev) } }

+static void unload_gpu(struct drm_device *dev) +{

• struct etnaviv_drm_private *priv = dev->dev_private;
  

• unsigned int i;
  

• for (i = 0; i < ETNA_MAX_PIPES; i++) {
  

•         struct etnaviv_gpu *g = priv->gpu[i];
  

•         if (g)
  

•                 etnaviv_gpu_shutdown(g);
  

• }
  

+}

static int etnaviv_open(struct drm_device *dev, struct drm_file *file) { struct etnaviv_drm_private *priv = dev->dev_private; @@ -581,6 +594,7 @@ static void etnaviv_unbind(struct device *dev) struct drm_device *drm = dev_get_drvdata(dev); struct etnaviv_drm_private *priv = drm->dev_private;

• unload_gpu(drm);
  drm_dev_unregister(drm);
  
  component_unbind_all(dev, drm);
  

diff --git a/drivers/gpu/drm/etnaviv/etnaviv_gpu.c b/drivers/gpu/drm/etnaviv/etnaviv_gpu.c index a31eeff2b297..1f0eb7e00657 100644 --- a/drivers/gpu/drm/etnaviv/etnaviv_gpu.c +++ b/drivers/gpu/drm/etnaviv/etnaviv_gpu.c @@ -714,6 +714,28 @@ static void etnaviv_gpu_hw_init(struct etnaviv_gpu *gpu) gpu_write(gpu, VIVS_HI_INTR_ENBL, ~0U); }

+static void etnaviv_loadavg_function(struct timer_list *t) +{

• struct etnaviv_gpu *gpu = from_timer(gpu, t, loadavg_timer);
  

• const u32 idle = gpu_read(gpu, VIVS_HI_IDLE_STATE);
  

This isn't guaranteed to work on a clock/power gated GPU. Also we surely don't want to wake a idle system every 10ms just to sample a "no load" value, so this needs some integration with runtime PM, to disable the sampling when the GPU is powered down and enable when powered up. The loadavg must be able to adapt to jumps in the sampling interval while idle.

Oh yea.. runtime PM.. I thought I was missing something. Will tackle this in the next version.

...

• int i;
  

• for (i = 0; i < ARRAY_SIZE(etna_idle_module_names); i++)
  

•         if ((idle & etna_idle_module_names[i].bit))
  

•                 sma_loadavg_add(&gpu->loadavg_value[i], 0);
  

•         else
  

•                 sma_loadavg_add(&gpu->loadavg_value[i], 100);
  

• spin_lock_bh(&gpu->loadavg_spinlock);
  

• for (i = 0; i < ARRAY_SIZE(etna_idle_module_names); i++)
  

•         gpu->loadavg_percentage[i] = sma_loadavg_read(&gpu->loadavg_value[i]);
  

• spin_unlock_bh(&gpu->loadavg_spinlock);
  

• mod_timer(t, jiffies + msecs_to_jiffies(10));
  

A jiffies based timer is much too coarse for a regular 10ms sampling. On a typical 100Hz system 10ms is a single jiffy, so your timer will fire anywhere in the range of ~0ms...~20ms. This won't get us a usable measurement.

Makes sense.. will switch to hrtimers.