[Intel-gfx] [PATCH v5 12/15] drm/i915/perf: Add OA unit support for Gen 8+

[Chris Wilson]

On Mon, Apr 24, 2017 at 12:17:48AM -0700, Lionel Landwerlin wrote:
> +static int gen8_configure_all_contexts(struct drm_i915_private *dev_priv)
> +{
> +	struct i915_gem_context *ctx;
> +	int ret;
> +
> +	ret = i915_mutex_lock_interruptible(&dev_priv->drm);
> +	if (ret)
> +		return ret;

Missed a switch to kernel context, to ensure that the last context is
also saved to memory.

> +
> +	/* The OA register config is setup through the context image. This image
> +	 * might be written to by the GPU on context switch (in particular on
> +	 * lite-restore). This means we can't safely update a context's image,
> +	 * if this context is scheduled/submitted to run on the GPU.
> +	 *
> +	 * We could emit the OA register config through the batch buffer but
> +	 * this might leave small interval of time where the OA unit is
> +	 * configured at an invalid sampling period.
> +	 *
> +	 * So far the best way to work around this issue seems to be draining
> +	 * the GPU from any submitted work.
> +	 */
> +        ret = i915_gem_wait_for_idle(dev_priv,
> +                                     I915_WAIT_INTERRUPTIBLE |
> +                                     I915_WAIT_LOCKED);
> +        if (ret) {
> +		mutex_unlock(&dev_priv->drm.struct_mutex);
> +                return ret;
> +	}
> +
> +	/* Since execlist submission may be happening asynchronously here then
> +	 * we first mark existing contexts dirty before we update the current
> +	 * context so if any switches happen in the middle we can expect
> +	 * that the act of scheduling will have itself ensured a consistent
> +	 * OA state update.
> +	 */
> +	list_for_each_entry(ctx, &dev_priv->context_list, link) {
> +		/* The actual update of the register state context will happen
> +		 * the next time this logical ring is submitted. (See
> +		 * i915_oa_update_reg_state() which hooks into
> +		 * execlists_update_context())
> +		 */
> +		atomic_set(&ctx->engine[RCS].oa_state_dirty, 1);

Considering that everything is now available to be modified, you can
change the contexts right here and now and remove the checks from the
much more common path.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre