[Intel-gfx] [PATCH 14/42] drm/i915: Use a radixtree for random access to the object's backing storage

[John Harrison]

On 07/10/2016 10:46, Chris Wilson wrote:
> A while ago we switched from a contiguous array of pages into an sglist,
> for that was both more convenient for mapping to hardware and avoided
> the requirement for a vmalloc array of pages on every object. However,
> certain GEM API calls (like pwrite, pread as well as performing
> relocations) do desire access to individual struct pages. A quick hack
> was to introduce a cache of the last access such that finding the
> following page was quick - this works so long as the caller desired
> sequential access. Walking backwards, or multiple callers, still hits a
> slow linear search for each page. One solution is to store each
> successful lookup in a radix tree.
>
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> ---
>   drivers/gpu/drm/i915/i915_drv.h         |  57 ++++--------
>   drivers/gpu/drm/i915/i915_gem.c         | 149 ++++++++++++++++++++++++++++----
>   drivers/gpu/drm/i915/i915_gem_stolen.c  |   4 +-
>   drivers/gpu/drm/i915/i915_gem_userptr.c |   4 +-
>   4 files changed, 154 insertions(+), 60 deletions(-)

Am curious to know if you have any performance data to show how much of 
a benefit this is? Are there any real world apps that would notice or 
just IGT benchmarks?

Reviewed-by: John Harrison <john.c.harrison at intel.com>

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