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

[Rob Clark]

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
> >
> > _______________________________________________
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> > mesa-dev at lists.freedesktop.org
> > https://lists.freedesktop.org/mailman/listinfo/mesa-dev
>
>
>