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    SubjectRe: GEM-related desktop sluggishness due to linear-time arch_get_unmapped_area_topdown()
    Am Dienstag, den 29.03.2011, 11:23 -0400 schrieb Jerome Glisse:
    > 2011/3/29 r6144 <>:
    > > 在 2011-03-29二的 10:22 -0400,Jerome Glisse写道:
    > >
    > >> Killer solution would be to have no mapping and a decent
    > >> upload/download ioctl that can take userpage.
    > >
    > > Doesn't this sound like GEM's read/write interface implemented by e.g.
    > > the i915 driver? But if I understand correctly, a mmap-like interface
    > > should still be necessary if we want to implement e.g. glMapBuffer()
    > > without extra copying.
    > >
    > > r6144
    > >
    > >
    > glMapBuffer should not be use, it's really not a good way to do stuff.
    > Anyway the extra copy might be unavoidable given that sometime the
    > front/back might either be in unmappable vram or either have memory
    > layout that is not the one specify at buffer creation (this is very
    > common when using tiling for instance). So even considering MapBuffer
    > or a like function i believe it's a lot better to not allow buffer
    > mapping in userspace but provide upload/download hooks that can use
    > userpage to avoid as much as possible extra copy.
    > Cheers,
    > Jerome

    Wouldn't this give us a performance penalty for short lived resources
    like vbo's which are located in GART memory? Mmap allows us to write
    directly to this drm controlled portion of sysram. With a copy based
    implementation we would have to allocate the buffer in sysram just to
    copy it over to another portion of sysram which seems a little insane to
    me, but I'm not an expert here.

    -- Lucas

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