Re: [PATCH 5/6] drm/i915: Do remaps for all contexts

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Tue, Sep 17, 2013 at 09:12:46PM -0700, Ben Widawsky wrote:
> On both Ivybridge and Haswell, row remapping information is saved and
> restored with context. This means, we never actually properly supported
> the l3 remapping because our sysfs interface is asynchronous (and not
> tied to any context), and the known faulty HW would be reused by the
> next context to run.
> 
> Not that due to the asynchronous nature of the sysfs entry, there is no
> point modifying the registers for the existing context. Instead we set a
> flag for all contexts to load the correct remapping information on the
> next run. Interested clients can use debugfs to determine whether or not
> the row has been remapped.
> 
> One could propose at this point that we just do the remapping in the
> kernel. I guess since we have to maintain the sysfs interface anyway,
> I'm not sure how useful it is, and I do like keeping the policy in
> userspace; (it wasn't my original decision to make the
> interface the way it is, so I'm not attached).
> 
> v2: Force a context switch when we have a remap on the next switch.
> (Ville)
> Don't let userspace use the interface with disabled contexts.
> 
> Signed-off-by: Ben Widawsky <ben@bwidawsk.net>
> ---
>  drivers/gpu/drm/i915/i915_debugfs.c     |  8 +++++++
>  drivers/gpu/drm/i915/i915_drv.h         |  1 +
>  drivers/gpu/drm/i915/i915_gem_context.c | 22 ++++++++++++++++----
>  drivers/gpu/drm/i915/i915_sysfs.c       | 37 +++++++++++++--------------------
>  4 files changed, 41 insertions(+), 27 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_debugfs.c b/drivers/gpu/drm/i915/i915_debugfs.c
> index ada0950..80bed69 100644
> --- a/drivers/gpu/drm/i915/i915_debugfs.c
> +++ b/drivers/gpu/drm/i915/i915_debugfs.c
> @@ -145,6 +145,13 @@ describe_obj(struct seq_file *m, struct drm_i915_gem_object *obj)
>  		seq_printf(m, " (%s)", obj->ring->name);
>  }
>  
> +static void describe_ctx(struct seq_file *m, struct i915_hw_context *ctx)
> +{
> +	seq_putc(m, ctx->is_initialized ? 'I' : 'i');
> +	seq_putc(m, ctx->remap_slice ? 'R' : 'r');
> +	seq_putc(m, ' ');
> +}
> +
>  static int i915_gem_object_list_info(struct seq_file *m, void *data)
>  {
>  	struct drm_info_node *node = (struct drm_info_node *) m->private;
> @@ -1463,6 +1470,7 @@ static int i915_context_status(struct seq_file *m, void *unused)
>  
>  	list_for_each_entry(ctx, &dev_priv->context_list, link) {
>  		seq_puts(m, "HW context ");
> +		describe_ctx(m, ctx);
>  		for_each_ring(ring, dev_priv, i)
>  			if (ring->default_context == ctx)
>  				seq_printf(m, "(default context %s) ", ring->name);
> diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
> index 1795927..015df52 100644
> --- a/drivers/gpu/drm/i915/i915_drv.h
> +++ b/drivers/gpu/drm/i915/i915_drv.h
> @@ -601,6 +601,7 @@ struct i915_hw_context {
>  	struct kref ref;
>  	int id;
>  	bool is_initialized;
> +	uint8_t remap_slice;
>  	struct drm_i915_file_private *file_priv;
>  	struct intel_ring_buffer *ring;
>  	struct drm_i915_gem_object *obj;
> diff --git a/drivers/gpu/drm/i915/i915_gem_context.c b/drivers/gpu/drm/i915/i915_gem_context.c
> index 2bbdce8..7e138cc 100644
> --- a/drivers/gpu/drm/i915/i915_gem_context.c
> +++ b/drivers/gpu/drm/i915/i915_gem_context.c
> @@ -140,7 +140,7 @@ create_hw_context(struct drm_device *dev,
>  {
>  	struct drm_i915_private *dev_priv = dev->dev_private;
>  	struct i915_hw_context *ctx;
> -	int ret;
> +	int ret, i;
>  
>  	ctx = kzalloc(sizeof(*ctx), GFP_KERNEL);
>  	if (ctx == NULL)
> @@ -181,6 +181,8 @@ create_hw_context(struct drm_device *dev,
>  
>  	ctx->file_priv = file_priv;
>  	ctx->id = ret;
> +	for (i = 0; i < NUM_L3_SLICES(dev); i++)
> +		ctx->remap_slice |= 1 << 1;
                                         ^

Still broken.

>  
>  	return ctx;
>  
> @@ -396,11 +398,11 @@ static int do_switch(struct i915_hw_context *to)
>  	struct intel_ring_buffer *ring = to->ring;
>  	struct i915_hw_context *from = ring->last_context;
>  	u32 hw_flags = 0;
> -	int ret;
> +	int ret, i;
>  
>  	BUG_ON(from != NULL && from->obj != NULL && from->obj->pin_count == 0);
>  
> -	if (from == to)
> +	if (from == to && !to->remap_slice)
>  		return 0;
>  
>  	ret = i915_gem_obj_ggtt_pin(to->obj, CONTEXT_ALIGN, false, false);
> @@ -423,7 +425,7 @@ static int do_switch(struct i915_hw_context *to)
>  
>  	if (!to->is_initialized || is_default_context(to))
>  		hw_flags |= MI_RESTORE_INHIBIT;
> -	else if (WARN_ON_ONCE(from == to)) /* not yet expected */
> +	else if (from == to)
>  		hw_flags |= MI_FORCE_RESTORE;

Hmm. Why do we need to restore actually? Could just leave MI_SET_CONTEXT
to be effectively a nop I think.

>  
>  	ret = mi_set_context(ring, to, hw_flags);
> @@ -432,6 +434,18 @@ static int do_switch(struct i915_hw_context *to)
>  		return ret;
>  	}
>  
> +	for (i = 0; i < MAX_L3_SLICES; i++) {
> +		if (!(to->remap_slice & (1<<i)))
> +			continue;
> +
> +		ret = i915_gem_l3_remap(ring, i);
> +		if (!ret) {
> +			to->remap_slice &= ~(1<<i);
> +			/* If it failed, try again next round */
> +			DRM_DEBUG_DRIVER("L3 remapping failed\n");
> +		}

The debug message is on the wrong branch.

> +	}
> +
>  	/* The backing object for the context is done after switching to the
>  	 * *next* context. Therefore we cannot retire the previous context until
>  	 * the next context has already started running. In fact, the below code
> diff --git a/drivers/gpu/drm/i915/i915_sysfs.c b/drivers/gpu/drm/i915/i915_sysfs.c
> index b07bdfb..deb8787 100644
> --- a/drivers/gpu/drm/i915/i915_sysfs.c
> +++ b/drivers/gpu/drm/i915/i915_sysfs.c
> @@ -118,9 +118,8 @@ i915_l3_read(struct file *filp, struct kobject *kobj,
>  	struct drm_minor *dminor = container_of(dev, struct drm_minor, kdev);
>  	struct drm_device *drm_dev = dminor->dev;
>  	struct drm_i915_private *dev_priv = drm_dev->dev_private;
> -	uint32_t misccpctl;
>  	int slice = (int)(uintptr_t)attr->private;
> -	int i, ret;
> +	int ret;
>  
>  	count = round_down(count, 4);
>  
> @@ -134,26 +133,13 @@ i915_l3_read(struct file *filp, struct kobject *kobj,
>  	if (ret)
>  		return ret;
>  
> -	if (IS_HASWELL(drm_dev)) {
> -		if (dev_priv->l3_parity.remap_info[slice])
> -			memcpy(buf,
> -			       dev_priv->l3_parity.remap_info[slice] + (offset/4),
> -			       count);
> -		else
> -			memset(buf, 0, count);
> -
> -		goto out;
> -	}
> -
> -	misccpctl = I915_READ(GEN7_MISCCPCTL);
> -	I915_WRITE(GEN7_MISCCPCTL, misccpctl & ~GEN7_DOP_CLOCK_GATE_ENABLE);
> -
> -	for (i = 0; i < count; i += 4)
> -		*((uint32_t *)(&buf[i])) = I915_READ(GEN7_L3LOG_BASE + offset + i);
> -
> -	I915_WRITE(GEN7_MISCCPCTL, misccpctl);
> +	if (dev_priv->l3_parity.remap_info[slice])
> +		memcpy(buf,
> +		       dev_priv->l3_parity.remap_info[slice] + (offset/4),
> +		       count);
> +	else
> +		memset(buf, 0, count);
>  
> -out:
>  	mutex_unlock(&drm_dev->struct_mutex);
>  
>  	return count;
> @@ -168,6 +154,7 @@ i915_l3_write(struct file *filp, struct kobject *kobj,
>  	struct drm_minor *dminor = container_of(dev, struct drm_minor, kdev);
>  	struct drm_device *drm_dev = dminor->dev;
>  	struct drm_i915_private *dev_priv = drm_dev->dev_private;
> +	struct i915_hw_context *ctx;
>  	u32 *temp = NULL; /* Just here to make handling failures easy */
>  	int slice = (int)(uintptr_t)attr->private;
>  	int ret;
> @@ -176,6 +163,9 @@ i915_l3_write(struct file *filp, struct kobject *kobj,
>  	if (ret)
>  		return ret;
>  
> +	if (dev_priv->hw_contexts_disabled)
> +		return -ENXIO;
> +
>  	ret = i915_mutex_lock_interruptible(drm_dev);
>  	if (ret)
>  		return ret;
> @@ -204,8 +194,9 @@ i915_l3_write(struct file *filp, struct kobject *kobj,
>  
>  	memcpy(dev_priv->l3_parity.remap_info[slice] + (offset/4), buf, count);
>  
> -	if (i915_gem_l3_remap(&dev_priv->ring[RCS], slice))
> -		count = 0;
> +	/* NB: We defer the remapping until we switch to the context */
> +	list_for_each_entry(ctx, &dev_priv->context_list, link)
> +		ctx->remap_slice |= (1<<slice);
>  
>  	mutex_unlock(&drm_dev->struct_mutex);
>  
> -- 
> 1.8.4
> 
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-- 
Ville Syrjälä
Intel OTC