Re: [CI 1/5] drm/i915: Allow disabling error capture

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On Tue, Oct 11, 2016 at 01:16:42PM +0300, Jani Nikula wrote:
> On Tue, 11 Oct 2016, Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> wrote:
> > On Tue, Oct 11, 2016 at 12:52:00PM +0300, Jani Nikula wrote:
> >> On Tue, 11 Oct 2016, Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> wrote:
> >> > We currently capture the GPU state after we detect a hang. This is vital
> >> > for us to both triage and debug hangs in the wild (post-mortem
> >> > debugging). However, it comes at the cost of running some potentially
> >> > dangerous code (since it has to make very few assumption about the state
> >> > of the driver) that is quite resource intensive.
> >> >
> >> > Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> >> > Reviewed-by: Joonas Lahtinen <joonas.lahtinen@xxxxxxxxxxxxxxx>
> >> > ---
> >> >  drivers/gpu/drm/i915/Kconfig          | 10 ++++++++++
> >> >  drivers/gpu/drm/i915/i915_debugfs.c   |  6 ++++++
> >> >  drivers/gpu/drm/i915/i915_drv.h       | 16 ++++++++++++++++
> >> >  drivers/gpu/drm/i915/i915_gpu_error.c |  7 +++++++
> >> >  drivers/gpu/drm/i915/i915_params.c    |  9 +++++++++
> >> >  drivers/gpu/drm/i915/i915_params.h    |  1 +
> >> >  drivers/gpu/drm/i915/i915_sysfs.c     |  8 ++++++++
> >> >  drivers/gpu/drm/i915/intel_display.c  |  4 ++++
> >> >  drivers/gpu/drm/i915/intel_overlay.c  |  4 ++++
> >> >  9 files changed, 65 insertions(+)
> >> >
> >> > diff --git a/drivers/gpu/drm/i915/Kconfig b/drivers/gpu/drm/i915/Kconfig
> >> > index 7769e469118f..10a6ac11b6a9 100644
> >> > --- a/drivers/gpu/drm/i915/Kconfig
> >> > +++ b/drivers/gpu/drm/i915/Kconfig
> >> > @@ -46,6 +46,16 @@ config DRM_I915_PRELIMINARY_HW_SUPPORT
> >> >  
> >> >  	  If in doubt, say "N".
> >> >  
> >> > +config DRM_I915_CAPTURE_ERROR
> >> > +	bool "Enable capturing GPU state following a hang"
> >> > +	depends on DRM_I915
> >> > +	default y
> >> > +	help
> >> > +	  This option enables capturing the GPU state when a hang is detected.
> >> > +	  This information is vital for triaging hangs and assists in debugging.
> >> > +
> >> > +	  If in doubt, say "Y".
> >> > +
> >> >  config DRM_I915_USERPTR
> >> >  	bool "Always enable userptr support"
> >> >  	depends on DRM_I915
> >> > diff --git a/drivers/gpu/drm/i915/i915_debugfs.c b/drivers/gpu/drm/i915/i915_debugfs.c
> >> > index 20689f1cd719..e4b5ba771bea 100644
> >> > --- a/drivers/gpu/drm/i915/i915_debugfs.c
> >> > +++ b/drivers/gpu/drm/i915/i915_debugfs.c
> >> > @@ -960,6 +960,8 @@ static int i915_hws_info(struct seq_file *m, void *data)
> >> >  	return 0;
> >> >  }
> >> >  
> >> > +#ifdef CONFIG_DRM_I915_CAPTURE_ERROR
> >> > +
> >> >  static ssize_t
> >> >  i915_error_state_write(struct file *filp,
> >> >  		       const char __user *ubuf,
> >> > @@ -1042,6 +1044,8 @@ static const struct file_operations i915_error_state_fops = {
> >> >  	.release = i915_error_state_release,
> >> >  };
> >> >  
> >> > +#endif
> >> > +
> >> >  static int
> >> >  i915_next_seqno_get(void *data, u64 *val)
> >> >  {
> >> > @@ -5398,7 +5402,9 @@ static const struct i915_debugfs_files {
> >> >  	{"i915_ring_missed_irq", &i915_ring_missed_irq_fops},
> >> >  	{"i915_ring_test_irq", &i915_ring_test_irq_fops},
> >> >  	{"i915_gem_drop_caches", &i915_drop_caches_fops},
> >> > +#ifdef CONFIG_DRM_I915_CAPTURE_ERROR
> >> >  	{"i915_error_state", &i915_error_state_fops},
> >> > +#endif
> >> >  	{"i915_next_seqno", &i915_next_seqno_fops},
> >> >  	{"i915_display_crc_ctl", &i915_display_crc_ctl_fops},
> >> >  	{"i915_pri_wm_latency", &i915_pri_wm_latency_fops},
> >> > diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
> >> > index 54d860e1c0fc..4570c4fa0287 100644
> >> > --- a/drivers/gpu/drm/i915/i915_drv.h
> >> > +++ b/drivers/gpu/drm/i915/i915_drv.h
> >> > @@ -3544,6 +3544,8 @@ static inline void intel_display_crc_init(struct drm_i915_private *dev_priv) {}
> >> >  #endif
> >> >  
> >> >  /* i915_gpu_error.c */
> >> > +#ifdef CONFIG_DRM_I915_CAPTURE_ERROR
> >> > +
> >> >  __printf(2, 3)
> >> >  void i915_error_printf(struct drm_i915_error_state_buf *e, const char *f, ...);
> >> >  int i915_error_state_to_str(struct drm_i915_error_state_buf *estr,
> >> > @@ -3564,6 +3566,20 @@ void i915_error_state_get(struct drm_device *dev,
> >> >  void i915_error_state_put(struct i915_error_state_file_priv *error_priv);
> >> >  void i915_destroy_error_state(struct drm_device *dev);
> >> >  
> >> > +#else
> >> > +
> >> > +static inline void i915_capture_error_state(struct drm_i915_private *dev_priv,
> >> > +					    u32 engine_mask,
> >> > +					    const char *error_msg)
> >> > +{
> >> > +}
> >> > +
> >> > +static inline void i915_destroy_error_state(struct drm_device *dev)
> >> > +{
> >> > +}
> >> > +
> >> > +#endif
> >> > +
> >> >  void i915_get_engine_instdone(struct drm_i915_private *dev_priv,
> >> >  			      enum intel_engine_id engine_id,
> >> >  			      struct intel_instdone *instdone);
> >> > diff --git a/drivers/gpu/drm/i915/i915_gpu_error.c b/drivers/gpu/drm/i915/i915_gpu_error.c
> >> > index b5b58692ac5a..9b395ffa3b6a 100644
> >> > --- a/drivers/gpu/drm/i915/i915_gpu_error.c
> >> > +++ b/drivers/gpu/drm/i915/i915_gpu_error.c
> >> > @@ -30,6 +30,8 @@
> >> >  #include <generated/utsrelease.h>
> >> >  #include "i915_drv.h"
> >> >  
> >> > +#ifdef CONFIG_DRM_I915_CAPTURE_ERROR
> >> > +
> >> >  static const char *engine_str(int engine)
> >> >  {
> >> >  	switch (engine) {
> >> > @@ -1464,6 +1466,9 @@ void i915_capture_error_state(struct drm_i915_private *dev_priv,
> >> >  	struct drm_i915_error_state *error;
> >> >  	unsigned long flags;
> >> >  
> >> > +	if (!i915.error_capture)
> >> > +		return;
> >> > +
> >> >  	if (READ_ONCE(dev_priv->gpu_error.first_error))
> >> >  		return;
> >> >  
> >> > @@ -1549,6 +1554,8 @@ void i915_destroy_error_state(struct drm_device *dev)
> >> >  		kref_put(&error->ref, i915_error_state_free);
> >> >  }
> >> >  
> >> > +#endif
> >> > +
> >> >  const char *i915_cache_level_str(struct drm_i915_private *i915, int type)
> >> >  {
> >> >  	switch (type) {
> >> > diff --git a/drivers/gpu/drm/i915/i915_params.c b/drivers/gpu/drm/i915/i915_params.c
> >> > index 768ad89d9cd4..e72a41223535 100644
> >> > --- a/drivers/gpu/drm/i915/i915_params.c
> >> > +++ b/drivers/gpu/drm/i915/i915_params.c
> >> > @@ -47,6 +47,7 @@ struct i915_params i915 __read_mostly = {
> >> >  	.load_detect_test = 0,
> >> >  	.force_reset_modeset_test = 0,
> >> >  	.reset = true,
> >> > +	.error_capture = true,
> >> >  	.invert_brightness = 0,
> >> >  	.disable_display = 0,
> >> >  	.enable_cmd_parser = 1,
> >> > @@ -115,6 +116,14 @@ MODULE_PARM_DESC(vbt_sdvo_panel_type,
> >> >  module_param_named_unsafe(reset, i915.reset, bool, 0600);
> >> >  MODULE_PARM_DESC(reset, "Attempt GPU resets (default: true)");
> >> >  
> >> > +#ifdef CONFIG_DRM_I915_CAPTURE_ERROR
> >> > +module_param_named(error_capture, i915.error_capture, bool, 0600);
> >> > +MODULE_PARM_DESC(error_capture,
> >> > +	"Record the GPU state following a hang. "
> >> > +	"This information in /sys/class/drm/card<N>/error is vital for "
> >> > +	"triaging and debugging hangs.");
> >> > +#endif
> >> 
> >> The addition of the module parameter is really orthogonal to the config
> >> option, and should be added separately.
> >> 
> >> The question is, what is the target audience of
> >> CONFIG_DRM_I915_CAPTURE_ERROR=n? Is the added config #ifdeffery worth
> >> the trouble? It *is* a maintainability burden, because we will only ever
> >> be building with CONFIG_DRM_I915_CAPTURE_ERROR=y ourselves, and we'll
> >> screw it up anyway. Does i915.error_capture=0 accomplish the same thing
> >> (apart from not reducing code size)? Do we really need to be able to
> >> prevent the root from enabling error capture on the fly?
> >
> > What I had in mind was that RT kernels will probably default to turning
> > off this facility (since it will cause latencies in the hundreds of ms
> > range).
> >  
> >> What would be wrong with just adding the module parameter, and making
> >> CONFIG_DRM_I915_CAPTURE_ERROR the default value for it? I.e.
> >> 
> >> 	.error_capture = IS_ENABLED(CONFIG_DRM_I915_CAPTURE_ERROR),
> >> 
> >> in the initialization. No #ifdefs anywhere.
> >
> > I wanted to turn it off by default at compilation time.
> 
> What I suggest above does that. ;)

It's 30KiB of code that they don't want. I know that's only about 3% of
the size of the driver, but it's a help.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre
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