[PATCH v4 8/9] gpu/drm/i915: optimize out the case when a range is updated to read only

[Joonas Lahtinen]

Hi Jerome,

This patch seems to have plenty of Cc:s, but none of the right ones :)

For further iterations, I guess you could use git option --cc to make
sure everyone gets the whole series, and still keep the Cc:s in the
patches themselves relevant to subsystems.

This doesn't seem to be on top of drm-tip, but on top of your previous
patches(?) that I had some comments about. Could you take a moment to
first address the couple of question I had, before proceeding to discuss
what is built on top of that base.

My reply's Message-ID is:
154289518994.19402.3481838548028068213 at jlahtine-desk.ger.corp.intel.com

Regards, Joonas

PS. Please keep me Cc:d in the following patches, I'm keen on
understanding the motive and benefits.

Quoting jglisse at redhat.com (2019-01-24 00:23:14)
> From: Jérôme Glisse <jglisse at redhat.com>
> 
> When range of virtual address is updated read only and corresponding
> user ptr object are already read only it is pointless to do anything.
> Optimize this case out.
> 
> Signed-off-by: Jérôme Glisse <jglisse at redhat.com>
> Cc: Christian König <christian.koenig at amd.com>
> Cc: Jan Kara <jack at suse.cz>
> Cc: Felix Kuehling <Felix.Kuehling at amd.com>
> Cc: Jason Gunthorpe <jgg at mellanox.com>
> Cc: Andrew Morton <akpm at linux-foundation.org>
> Cc: Matthew Wilcox <mawilcox at microsoft.com>
> Cc: Ross Zwisler <zwisler at kernel.org>
> Cc: Dan Williams <dan.j.williams at intel.com>
> Cc: Paolo Bonzini <pbonzini at redhat.com>
> Cc: Radim Krčmář <rkrcmar at redhat.com>
> Cc: Michal Hocko <mhocko at kernel.org>
> Cc: Ralph Campbell <rcampbell at nvidia.com>
> Cc: John Hubbard <jhubbard at nvidia.com>
> Cc: kvm at vger.kernel.org
> Cc: dri-devel at lists.freedesktop.org
> Cc: linux-rdma at vger.kernel.org
> Cc: linux-fsdevel at vger.kernel.org
> Cc: Arnd Bergmann <arnd at arndb.de>
> ---
>  drivers/gpu/drm/i915/i915_gem_userptr.c | 16 ++++++++++++++++
>  1 file changed, 16 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/i915_gem_userptr.c b/drivers/gpu/drm/i915/i915_gem_userptr.c
> index 9558582c105e..23330ac3d7ea 100644
> --- a/drivers/gpu/drm/i915/i915_gem_userptr.c
> +++ b/drivers/gpu/drm/i915/i915_gem_userptr.c
> @@ -59,6 +59,7 @@ struct i915_mmu_object {
>         struct interval_tree_node it;
>         struct list_head link;
>         struct work_struct work;
> +       bool read_only;
>         bool attached;
>  };
>  
> @@ -119,6 +120,7 @@ static int i915_gem_userptr_mn_invalidate_range_start(struct mmu_notifier *_mn,
>                 container_of(_mn, struct i915_mmu_notifier, mn);
>         struct i915_mmu_object *mo;
>         struct interval_tree_node *it;
> +       bool update_to_read_only;
>         LIST_HEAD(cancelled);
>         unsigned long end;
>  
> @@ -128,6 +130,8 @@ static int i915_gem_userptr_mn_invalidate_range_start(struct mmu_notifier *_mn,
>         /* interval ranges are inclusive, but invalidate range is exclusive */
>         end = range->end - 1;
>  
> +       update_to_read_only = mmu_notifier_range_update_to_read_only(range);
> +
>         spin_lock(&mn->lock);
>         it = interval_tree_iter_first(&mn->objects, range->start, end);
>         while (it) {
> @@ -145,6 +149,17 @@ static int i915_gem_userptr_mn_invalidate_range_start(struct mmu_notifier *_mn,
>                  * object if it is not in the process of being destroyed.
>                  */
>                 mo = container_of(it, struct i915_mmu_object, it);
> +
> +               /*
> +                * If it is already read only and we are updating to
> +                * read only then we do not need to change anything.
> +                * So save time and skip this one.
> +                */
> +               if (update_to_read_only && mo->read_only) {
> +                       it = interval_tree_iter_next(it, range->start, end);
> +                       continue;
> +               }
> +
>                 if (kref_get_unless_zero(&mo->obj->base.refcount))
>                         queue_work(mn->wq, &mo->work);
>  
> @@ -270,6 +285,7 @@ i915_gem_userptr_init__mmu_notifier(struct drm_i915_gem_object *obj,
>         mo->mn = mn;
>         mo->obj = obj;
>         mo->it.start = obj->userptr.ptr;
> +       mo->read_only = i915_gem_object_is_readonly(obj);
>         mo->it.last = obj->userptr.ptr + obj->base.size - 1;
>         INIT_WORK(&mo->work, cancel_userptr);
>  
> -- 
> 2.17.2
> 
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