Re: [CI 2/2] drm/i915: Initialize legacy semaphores from engine hw id indexed array

Tvrtko Ursulin
2016-08-17T09:34:21Z

On 16/08/16 17:18, Chris Wilson wrote:
> On Tue, Aug 16, 2016 at 05:04:21PM +0100, Tvrtko Ursulin wrote:
>> From: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
>>
>> Build the legacy semaphore initialisation array using the engine
>> hardware ids instead of driver internal ones. This makes the
>> static array size dependent only on the number of gen6 semaphore
>> engines.
>>
>> Also makes the per-engine semaphore wait and signal tables
>> hardware id indexed saving some more space.
>>
>> v2: Refactor I915_GEN6_NUM_ENGINES to GEN6_SEMAPHORE_LAST. (Chris Wilson)
>> v3: More polish. (Chris Wilson)
>>
>> Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
>> Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
>> ---
>> drivers/gpu/drm/i915/intel_ringbuffer.c | 55 +++++++++++++++++----------------
>> drivers/gpu/drm/i915/intel_ringbuffer.h | 7 +++--
>> 2 files changed, 34 insertions(+), 28 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c b/drivers/gpu/drm/i915/intel_ringbuffer.c
>> index fa22bd87bab0..12703ea27259 100644
>> --- a/drivers/gpu/drm/i915/intel_ringbuffer.c
>> +++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
>> @@ -1337,8 +1337,7 @@ static int gen6_signal(struct drm_i915_gem_request *req)
>> {
>> struct intel_ring *ring = req->ring;
>> struct drm_i915_private *dev_priv = req->i915;
>> - struct intel_engine_cs *useless;
>> - enum intel_engine_id id;
>> + struct intel_engine_cs *engine;
>> int ret, num_rings;
>>
>> num_rings = INTEL_INFO(dev_priv)->num_rings;
>> @@ -1346,9 +1345,13 @@ static int gen6_signal(struct drm_i915_gem_request *req)
>> if (ret)
>> return ret;
>>
>> - for_each_engine_id(useless, dev_priv, id) {
>> - i915_reg_t mbox_reg = req->engine->semaphore.mbox.signal[id];
>> + for_each_engine(engine, dev_priv) {
>> + i915_reg_t mbox_reg;
>> +
>> + if (!(BIT(engine->hw_id) & GEN6_SEMAPHORES_MASK))
>> + continue;
>
> Later on, it would be nice if this used
> for_each_engine_masked()
> instead (presupposing we have an efficient iterator for a sparse mask).
> The issue is in defining GEN6_SEMAPHORES_MASK
>
> #define GEN6_SEMAPHORES_MASK \
> (RENDER_RING |
> BSD_RING |
> BSD2_RING |
> BLT_RING |
> VECS_RING)
>
> Defnitely pencil that in for when otherwise we would iterate over 10
> empty slots in dev_priv->engines[].
>
> I'm thinking that we should make for_each_engine_mask() the default, say
> for_each_engine(engine, dev_priv, ALL_ENGINES, id)

Or add an initialized engine array to dev_priv, in addition to the
existing map for best of both worlds.

That would prevent churn in for_each_engine users.

Or just give up and add something smarter, like a typdef
intel_engine_it, to each of them and be done with churn once for all.

But we said there aren't any iterators on fast paths anyway so I would
rather we chose to do nothing. :)

Regards,

Tvrtko