[Intel-gfx] [PATCH 1/3] drm: Track drm_mm nodes with an interval tree

[Daniel, Thomas]

Hi,

> -----Original Message-----
> From: Intel-gfx [mailto:intel-gfx-bounces at lists.freedesktop.org] On Behalf Of
> David Herrmann
> Sent: Wednesday, October 7, 2015 11:23 AM
> To: Chris Wilson; Daniel Vetter; Intel Graphics Development; dri-
> devel at lists.freedesktop.org
> Subject: Re: [Intel-gfx] [PATCH 1/3] drm: Track drm_mm nodes with an interval
> tree
> 
> Hi
> 
> On Tue, Oct 6, 2015 at 1:19 PM, Chris Wilson <chris at chris-wilson.co.uk> wrote:
> > On Tue, Oct 06, 2015 at 01:11:56PM +0200, Daniel Vetter wrote:
> >> On Tue, Oct 06, 2015 at 11:53:09AM +0100, Chris Wilson wrote:
> >> > In addition to the last-in/first-out stack for accessing drm_mm nodes,
> >> > we occasionally and in the future often want to find a drm_mm_node by an
> >> > address. To do so efficiently we need to track the nodes in an interval
> >> > tree - lookups for a particular address will then be O(lg(N)), where N
> >> > is the number of nodes in the range manager as opposed to O(N).
> >> > Insertion however gains an extra O(lg(N)) step for all nodes
> >> > irrespective of whether the interval tree is in use. For future i915
> >> > patches, eliminating the linear walk is a significant improvement.
> >> >
> >> > Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> >> > Cc: dri-devel at lists.freedesktop.org
> >>
> >> For the vma manager David Herrman put the interval tree outside of
> drm_mm.
> >> Whichever way we pick, but I think we should be consistent about this.
> >
> > Given that the basis of this patch is that functionality exposed by
> > drm_mm (i.e. drm_mm_reserve_node) is too slow for our use case (i.e.
> > there is a measurable perf degradation if we switch over from the mru
> > stack to using fixed addresses) it makes sense to improve that
> > functionality. The question is then why the drm_vma_manager didn't use
> > and improve the existing functionality...
> 
> I didn't want to slow down drm_mm operations, so I kept it separate. I
> don't mind if it is merged into drm_mm. It'd be trivial to make the
> vma-manager use it (only on the top-level, though).
> 
> Thanks
> David

Is there a conclusion to this discussion?  I'm under increasing pressure to get the i915 soft-pinning merged and Chris's latest version depends on this interval tree.

I've been told to post a new rebase of the version which doesn't use the interval tree if not.

Cheers,
Thomas.