[Mesa-dev] [PATCH 6/9] i965: Map the query results for the life of the bo

[Kenneth Graunke]

On Wednesday, June 14, 2017 3:50:12 PM PDT Kenneth Graunke wrote:
> On Friday, June 9, 2017 6:01:37 AM PDT Chris Wilson wrote:
> > If we map the bo upon creation, we can avoid the latency of mmapping it
> > when querying, and later use the asynchronous, persistent map of the
> > predicate to do a quick query.
> > 
> > Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> > Cc: Kenneth Graunke <kenneth at whitecape.org>
> > Cc: Matt Turner <mattst88 at gmail.com>
> > ---
> >  src/mesa/drivers/dri/i965/brw_bufmgr.c    | 15 +++++++++++++
> >  src/mesa/drivers/dri/i965/brw_bufmgr.h    |  2 ++
> >  src/mesa/drivers/dri/i965/brw_context.h   |  1 +
> >  src/mesa/drivers/dri/i965/gen6_queryobj.c | 37 ++++++++++++++++++++++---------
> >  4 files changed, 44 insertions(+), 11 deletions(-)
> > 
> > diff --git a/src/mesa/drivers/dri/i965/brw_bufmgr.c b/src/mesa/drivers/dri/i965/brw_bufmgr.c
> > index 01590a0b0a..9028b538c6 100644
> > --- a/src/mesa/drivers/dri/i965/brw_bufmgr.c
> > +++ b/src/mesa/drivers/dri/i965/brw_bufmgr.c
> > @@ -775,6 +775,21 @@ brw_bo_map(struct brw_context *brw, struct brw_bo *bo, unsigned flags)
> >        return brw_bo_map_gtt(brw, bo, flags);
> >  }
> >  
> > +void
> > +brw_bo_map_sync(struct brw_context *brw, struct brw_bo *bo, unsigned flags)
> > +{
> > +   unsigned domain;
> > +
> > +   if (bo->tiling_mode != I915_TILING_NONE && !(flags & MAP_RAW))
> > +      domain = I915_GEM_DOMAIN_GTT;
> > +   else if (can_map_cpu(bo, flags))
> > +      domain = I915_GEM_DOMAIN_CPU;
> > +   else
> > +      domain = I915_GEM_DOMAIN_GTT;
> > +
> > +   set_domain(brw, __func__, bo, domain, flags & MAP_WRITE ? domain : 0);
> > +}
> > +
> >  int
> >  brw_bo_unmap(struct brw_bo *bo)
> >  {
> > diff --git a/src/mesa/drivers/dri/i965/brw_bufmgr.h b/src/mesa/drivers/dri/i965/brw_bufmgr.h
> > index 3a397be695..214b75bf1a 100644
> > --- a/src/mesa/drivers/dri/i965/brw_bufmgr.h
> > +++ b/src/mesa/drivers/dri/i965/brw_bufmgr.h
> > @@ -196,6 +196,8 @@ void brw_bo_unreference(struct brw_bo *bo);
> >   */
> >  MUST_CHECK void *brw_bo_map(struct brw_context *brw, struct brw_bo *bo, unsigned flags);
> >  
> > +void brw_bo_map_sync(struct brw_context *brw, struct brw_bo *bo, unsigned flags);
> > +
> >  /**
> >   * Reduces the refcount on the userspace mapping of the buffer
> >   * object.
> > diff --git a/src/mesa/drivers/dri/i965/brw_context.h b/src/mesa/drivers/dri/i965/brw_context.h
> > index c5acb83ad0..117b1ecdca 100644
> > --- a/src/mesa/drivers/dri/i965/brw_context.h
> > +++ b/src/mesa/drivers/dri/i965/brw_context.h
> > @@ -419,6 +419,7 @@ struct brw_query_object {
> >  
> >     /** Last query BO associated with this query. */
> >     struct brw_bo *bo;
> > +   uint64_t *results;
> >  
> >     /** Last index in bo with query data for this object. */
> >     int last_index;
> > diff --git a/src/mesa/drivers/dri/i965/gen6_queryobj.c b/src/mesa/drivers/dri/i965/gen6_queryobj.c
> > index f913f986ae..18af608166 100644
> > --- a/src/mesa/drivers/dri/i965/gen6_queryobj.c
> > +++ b/src/mesa/drivers/dri/i965/gen6_queryobj.c
> > @@ -221,7 +221,9 @@ gen6_queryobj_get_results(struct gl_context *ctx,
> >     if (query->bo == NULL)
> >        return;
> >  
> > -   uint64_t *results = brw_bo_map(brw, query->bo, MAP_READ);
> > +   brw_bo_map_sync(brw, query->bo, MAP_READ | MAP_COHERENT);
> > +   uint64_t *results = query->results;
> > +
> >     switch (query->Base.Target) {
> >     case GL_TIME_ELAPSED:
> >        /* The query BO contains the starting and ending timestamps.
> > @@ -296,7 +298,6 @@ gen6_queryobj_get_results(struct gl_context *ctx,
> >     default:
> >        unreachable("Unrecognized query target in brw_queryobj_get_results()");
> >     }
> > -   brw_bo_unmap(query->bo);
> >  
> >     /* Now that we've processed the data stored in the query's buffer object,
> >      * we can release it.
> > @@ -307,6 +308,23 @@ gen6_queryobj_get_results(struct gl_context *ctx,
> >     query->Base.Ready = true;
> >  }
> >  
> > +static int gen6_alloc_query(struct brw_context *brw,
> > +                            struct brw_query_object *query)
> > +{
> > +   /* Since we're starting a new query, we need to throw away old results. */
> > +   if (query->bo)
> > +      brw_bo_unreference(query->bo);
> > +
> > +   query->bo = brw_bo_alloc(brw->bufmgr, "query results", 4096, 4096);
> > +   query->results = brw_bo_map(brw, query->bo,
> > +                               MAP_READ | MAP_COHERENT | MAP_ASYNC);
> 
> I don't understand why you're using MAP_ASYNC here.  We're allocating a new
> BO here, and not using the BO_ALLOC_FOR_RENDER flag, so it will be idle.
> (brw_bufmgr.c:297 should ensure we never get a busy BO - if the cached BOs
> are busy, it will just allocate us a new one.)
> 
> So, MAP_ASYNC shouldn't avoid a stall.  It does, however, skip the
> SET_DOMAIN call, which means that it may not have the right domain
> for our new coherent mapping.  Hence, you need to whack it later with
> your new brw_bo_map_sync() helper.
> 
> I think you can drop MAP_ASYNC, and drop brw_bo_map_sync() entirely,
> with no ill-effects.  Or am I wrong?

D'oh, in fact I am wrong.  brw_bo_map_sync() is what stalls, allowing
WaitQuery() to wait until the counter snapshots actually land in the
buffer.  That's pretty darn important.

Now I'm just confused by all the domains.
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