On Tue, 11 Oct 2016, Chris Wilson <ch...@chris-wilson.co.uk> 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 <ch...@chris-wilson.co.uk>
> Reviewed-by: Joonas Lahtinen <joonas.lahti...@linux.intel.com>
> ---
>  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 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.

BR,
Jani.


> +
>  module_param_named_unsafe(enable_hangcheck, i915.enable_hangcheck, bool, 
> 0644);
>  MODULE_PARM_DESC(enable_hangcheck,
>       "Periodically check GPU activity for detecting hangs. "
> diff --git a/drivers/gpu/drm/i915/i915_params.h 
> b/drivers/gpu/drm/i915/i915_params.h
> index 3a0dd78ddb38..94efc899c1ef 100644
> --- a/drivers/gpu/drm/i915/i915_params.h
> +++ b/drivers/gpu/drm/i915/i915_params.h
> @@ -59,6 +59,7 @@ struct i915_params {
>       bool load_detect_test;
>       bool force_reset_modeset_test;
>       bool reset;
> +     bool error_capture;
>       bool disable_display;
>       bool verbose_state_checks;
>       bool nuclear_pageflip;
> diff --git a/drivers/gpu/drm/i915/i915_sysfs.c 
> b/drivers/gpu/drm/i915/i915_sysfs.c
> index 1012eeea1324..c9b71f676a57 100644
> --- a/drivers/gpu/drm/i915/i915_sysfs.c
> +++ b/drivers/gpu/drm/i915/i915_sysfs.c
> @@ -514,6 +514,8 @@ static const struct attribute *vlv_attrs[] = {
>       NULL,
>  };
>  
> +#ifdef CONFIG_DRM_I915_CAPTURE_ERROR
> +
>  static ssize_t error_state_read(struct file *filp, struct kobject *kobj,
>                               struct bin_attribute *attr, char *buf,
>                               loff_t off, size_t count)
> @@ -571,6 +573,8 @@ static struct bin_attribute error_state_attr = {
>       .write = error_state_write,
>  };
>  
> +#endif
> +
>  void i915_setup_sysfs(struct drm_i915_private *dev_priv)
>  {
>       struct device *kdev = dev_priv->drm.primary->kdev;
> @@ -617,17 +621,21 @@ void i915_setup_sysfs(struct drm_i915_private *dev_priv)
>       if (ret)
>               DRM_ERROR("RPS sysfs setup failed\n");
>  
> +#ifdef CONFIG_DRM_I915_CAPTURE_ERROR
>       ret = sysfs_create_bin_file(&kdev->kobj,
>                                   &error_state_attr);
>       if (ret)
>               DRM_ERROR("error_state sysfs setup failed\n");
> +#endif
>  }
>  
>  void i915_teardown_sysfs(struct drm_i915_private *dev_priv)
>  {
>       struct device *kdev = dev_priv->drm.primary->kdev;
>  
> +#ifdef CONFIG_DRM_I915_CAPTURE_ERROR
>       sysfs_remove_bin_file(&kdev->kobj, &error_state_attr);
> +#endif
>       if (IS_VALLEYVIEW(dev_priv) || IS_CHERRYVIEW(dev_priv))
>               sysfs_remove_files(&kdev->kobj, vlv_attrs);
>       else
> diff --git a/drivers/gpu/drm/i915/intel_display.c 
> b/drivers/gpu/drm/i915/intel_display.c
> index 23a6c7213eca..202812916b67 100644
> --- a/drivers/gpu/drm/i915/intel_display.c
> +++ b/drivers/gpu/drm/i915/intel_display.c
> @@ -17099,6 +17099,8 @@ int intel_modeset_vga_set_state(struct drm_device 
> *dev, bool state)
>       return 0;
>  }
>  
> +#ifdef CONFIG_DRM_I915_CAPTURE_ERROR
> +
>  struct intel_display_error_state {
>  
>       u32 power_well_driver;
> @@ -17281,3 +17283,5 @@ intel_display_print_error_state(struct 
> drm_i915_error_state_buf *m,
>               err_printf(m, "  VSYNC: %08x\n", error->transcoder[i].vsync);
>       }
>  }
> +
> +#endif
> diff --git a/drivers/gpu/drm/i915/intel_overlay.c 
> b/drivers/gpu/drm/i915/intel_overlay.c
> index a24bc8c7889f..7c392547711f 100644
> --- a/drivers/gpu/drm/i915/intel_overlay.c
> +++ b/drivers/gpu/drm/i915/intel_overlay.c
> @@ -1470,6 +1470,8 @@ void intel_cleanup_overlay(struct drm_i915_private 
> *dev_priv)
>       kfree(dev_priv->overlay);
>  }
>  
> +#ifdef CONFIG_DRM_I915_CAPTURE_ERROR
> +
>  struct intel_overlay_error_state {
>       struct overlay_registers regs;
>       unsigned long base;
> @@ -1587,3 +1589,5 @@ intel_overlay_print_error_state(struct 
> drm_i915_error_state_buf *m,
>       P(UVSCALEV);
>  #undef P
>  }
> +
> +#endif

-- 
Jani Nikula, Intel Open Source Technology Center
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