Linux userland API discussions

* Re: [RFC PATCH 07/11] drm/i915: Expose PMU for Observation Architecture
From: Robert Bragg @ 2015-05-18 16:21 UTC (permalink / raw)
  To: dri-devel, David Airlie, Daniel Vetter, Ingo Molnar,
	Peter Zijlstra, Paul Mackerras, Chris Wilson,
	Arnaldo Carvalho de Melo, intel-gfx, linux-api, linux-kernel
In-Reply-To: <20150507143639.GY22099@nuc-i3427.alporthouse.com>

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On 7 May 2015 15:37, "Chris Wilson" <chris@chris-wilson.co.uk> wrote:
>
> On Thu, May 07, 2015 at 03:15:50PM +0100, Robert Bragg wrote:
> > +static int init_oa_buffer(struct perf_event *event)
> > +{
> > +     struct drm_i915_private *dev_priv =
> > +             container_of(event->pmu, typeof(*dev_priv), oa_pmu.pmu);
> > +     struct drm_i915_gem_object *bo;
> > +     int ret;
> > +
> > +     BUG_ON(!IS_HASWELL(dev_priv->dev));
> > +     BUG_ON(!mutex_is_locked(&dev_priv->dev->struct_mutex));
> > +     BUG_ON(dev_priv->oa_pmu.oa_buffer.obj);
> > +
> > +     spin_lock_init(&dev_priv->oa_pmu.oa_buffer.flush_lock);
> > +
> > +     /* NB: We over allocate the OA buffer due to the way raw sample
data
> > +      * gets copied from the gpu mapped circular buffer into the perf
> > +      * circular buffer so that only one copy is required.
> > +      *
> > +      * For each perf sample (raw->size + 4) needs to be 8 byte
aligned,
> > +      * where the 4 corresponds to the 32bit raw->size member that's
> > +      * added to the sample header that userspace sees.
> > +      *
> > +      * Due to the + 4 for the size member: when we copy a report to
the
> > +      * userspace facing perf buffer we always copy an additional 4
bytes
> > +      * from the subsequent report to make up for the miss alignment,
but
> > +      * when a report is at the end of the gpu mapped buffer we need to
> > +      * read 4 bytes past the end of the buffer.
> > +      */
> > +     bo = i915_gem_alloc_object(dev_priv->dev, OA_BUFFER_SIZE +
PAGE_SIZE);
> > +     if (bo == NULL) {
> > +             DRM_ERROR("Failed to allocate OA buffer\n");
> > +             ret = -ENOMEM;
> > +             goto err;
> > +     }
> > +     dev_priv->oa_pmu.oa_buffer.obj = bo;
> > +
> > +     ret = i915_gem_object_set_cache_level(bo, I915_CACHE_LLC);
> > +     if (ret)
> > +             goto err_unref;
> > +
> > +     /* PreHSW required 512K alignment, HSW requires 16M */
> > +     ret = i915_gem_obj_ggtt_pin(bo, SZ_16M, 0);
> > +     if (ret)
> > +             goto err_unref;
> > +
> > +     dev_priv->oa_pmu.oa_buffer.gtt_offset =
i915_gem_obj_ggtt_offset(bo);
> > +     dev_priv->oa_pmu.oa_buffer.addr = vmap_oa_buffer(bo);
>
> You can look forward to both i915_gem_object_create_internal() and
> i915_gem_object_pin_vmap()

Okey, will do, thanks.

>
> > +
> > +     /* Pre-DevBDW: OABUFFER must be set with counters off,
> > +      * before OASTATUS1, but after OASTATUS2 */
> > +     I915_WRITE(GEN7_OASTATUS2, dev_priv->oa_pmu.oa_buffer.gtt_offset |
> > +                GEN7_OASTATUS2_GGTT); /* head */
> > +     I915_WRITE(GEN7_OABUFFER, dev_priv->oa_pmu.oa_buffer.gtt_offset);
> > +     I915_WRITE(GEN7_OASTATUS1, dev_priv->oa_pmu.oa_buffer.gtt_offset |
> > +                GEN7_OASTATUS1_OABUFFER_SIZE_16M); /* tail */
> > +
> > +     DRM_DEBUG_DRIVER("OA Buffer initialized, gtt offset = 0x%x, vaddr
= %p",
> > +                      dev_priv->oa_pmu.oa_buffer.gtt_offset,
> > +                      dev_priv->oa_pmu.oa_buffer.addr);
> > +
> > +     return 0;
> > +
> > +err_unref:
> > +     drm_gem_object_unreference_unlocked(&bo->base);
>
> But what I really what to say was:
> mutex deadlock^^^

Yikes, I've pushed an updated patch addressing this and can reply with a
new patch here in a bit.

Thanks,
- Robert

> -Chris
>
> --
> Chris Wilson, Intel Open Source Technology Centre

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