[Mesa-dev] [PATCH] util/slab: add slab_free_fast()

[Rob Clark]

should be easy enough to re-create..  I will note that the perf
results differ a *lot* if I pin things to small (in-order) calls, so
I'm guestimating that what perf is showing me w/ slab_free() is where
reality catches up to mis-predicted branches.

BR,
-R


On Wed, Aug 7, 2019 at 9:44 PM Jason Ekstrand <jason at jlekstrand.net> wrote:
>
> It'd be nice to throw some numbers in the donut message before you push.
> "Real" ones of it's convenient but what you have below is probably fine if
> you've already thrown the data away.
>
> On August 7, 2019 19:13:21 Rob Clark <robdclark at chromium.org> wrote:
>
> > Yes, although not in front of me.. overall for gl_driver2 it was
> > something along the lines of 2-3%.  Looking at perf-report, slab_free
> > (+ slab_free_fast) went from ~20% to nearly nothing(ish) iirc..
> >
> > BR,
> > -R
> >
> > On Wed, Aug 7, 2019 at 4:58 PM Jason Ekstrand <jason at jlekstrand.net> wrote:
> >>
> >> Do you have any actual numbers for this?
> >>
> >> On August 7, 2019 17:02:22 Rob Clark <robdclark at gmail.com> wrote:
> >>
> >> > From: Rob Clark <robdclark at chromium.org>
> >> >
> >> > I noticed slab_free() showing up at the top of perf results in
> >> > gl_driver2, due to "streaming" GPU state objects, which are allocated
> >> > and destroyed within a single draw call.
> >> >
> >> > In this case, it is guaranteed that we free on the same child pool,
> >> > from the same (only) thread accessing the child pool.  So add a faster,
> >> > but more restricted version of slab_free() to cut the overhead.
> >> >
> >> > Signed-off-by: Rob Clark <robdclark at chromium.org>
> >> > ---
> >> > src/util/slab.c | 20 ++++++++++++++++++++
> >> > src/util/slab.h |  1 +
> >> > 2 files changed, 21 insertions(+)
> >> >
> >> > diff --git a/src/util/slab.c b/src/util/slab.c
> >> > index 62634034fdc..21076a80238 100644
> >> > --- a/src/util/slab.c
> >> > +++ b/src/util/slab.c
> >> > @@ -276,6 +276,26 @@ void slab_free(struct slab_child_pool *pool, void *ptr)
> >> >    }
> >> > }
> >> >
> >> > +/**
> >> > + * Similar to slab_free(), except that freeing an object in a different pool
> >> > + * from the one it was allocated from is *not* allowed.
> >> > + */
> >> > +void slab_free_fast(struct slab_child_pool *pool, void *ptr)
> >> > +{
> >> > +   struct slab_element_header *elt = ((struct slab_element_header*)ptr - 1);
> >> > +
> >> > +   CHECK_MAGIC(elt, SLAB_MAGIC_ALLOCATED);
> >> > +   SET_MAGIC(elt, SLAB_MAGIC_FREE);
> >> > +
> >> > +   assert(p_atomic_read(&elt->owner) == (intptr_t)pool);
> >> > +
> >> > +   /* This is the simple case: The caller guarantees that we can safely
> >> > +    * access the free list.
> >> > +    */
> >> > +   elt->next = pool->free;
> >> > +   pool->free = elt;
> >> > +}
> >> > +
> >> > /**
> >> >  * Allocate an object from the slab. Single-threaded (no mutex).
> >> >  */
> >> > diff --git a/src/util/slab.h b/src/util/slab.h
> >> > index 5a25adaf7f4..9748cd95858 100644
> >> > --- a/src/util/slab.h
> >> > +++ b/src/util/slab.h
> >> > @@ -78,6 +78,7 @@ void slab_create_child(struct slab_child_pool *pool,
> >> > void slab_destroy_child(struct slab_child_pool *pool);
> >> > void *slab_alloc(struct slab_child_pool *pool);
> >> > void slab_free(struct slab_child_pool *pool, void *ptr);
> >> > +void slab_free_fast(struct slab_child_pool *pool, void *ptr);
> >> >
> >> > struct slab_mempool {
> >> >    struct slab_parent_pool parent;
> >> > --
> >> > 2.21.0
> >> >
> >> > _______________________________________________
> >> > mesa-dev mailing list
> >> > mesa-dev at lists.freedesktop.org
> >> > https://lists.freedesktop.org/mailman/listinfo/mesa-dev
> >>
> >>
> >>
>
>
>