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    SubjectRe: GEM-related desktop sluggishness due to linear-time arch_get_unmapped_area_topdown()
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    On Wed, Mar 30, 2011 at 10:07 AM, Chris Wilson <chris@chris-wilson.co.uk> wrote:
    > On Wed, 30 Mar 2011 09:28:07 -0400, Jerome Glisse <j.glisse@gmail.com> wrote:
    >> On Wed, Mar 30, 2011 at 3:32 AM, Chris Wilson <chris@chris-wilson.co.uk> wrote:
    >> > On Wed, 30 Mar 2011 07:57:49 +1000, Dave Airlie <airlied@gmail.com> wrote:
    >> >> On Wed, Mar 30, 2011 at 7:04 AM, Jerome Glisse <j.glisse@gmail.com> wrote:
    >> >> > What i had in mind was something little bit more advance that pwrite,
    >> >> > somethings that would take width,height,pitch of userpage and would be
    >> >> > able to perform proper blit. But yes pwrite in intel is kind of
    >> >> > limited.
    >> >>
    >> >> TTM has support for userpage binding we just don't use it.
    >> >
    >> > Yes, and I've been experimenting with the same in GEM to great effect in
    >> > the DDX. The complication remains in managing the CPU synchronisation,
    >> > which suggests that it would only be useful for STREAM_DRAW objects (and
    >> > perhaps the sub-region updates to STATIC_DRAW). (And for readback, if
    >> > retrieving the data were the actual bottleneck.)
    >>
    >> What do you mean by CPU synchronisation ? In what i had in mind the
    >> upload/download would block userspace until operation is, this would
    >> make upload/dowload barrier of course it doesn't play well with
    >> usecase where you keep uploading/downloading (idea to aleviate that is
    >> to allow several download/upload in one ioctl call).
    >
    > Yes, that is the issue: having to control access to the user pages whilst
    > they are in use by the GPU. A completely synchronous API for performing
    > a single pwrite with the blitter is too slow, much slower than doing an
    > uncached write with the CPU and queueing up multiple blits (as we
    > currently do).
    >
    > The API I ended up with for the pwrite using the BLT was to specify a 2D
    > region (addr, width, height, stride, flags etc) and list of clip rects. At
    > which point I grew disenchanted, and realised that simply creating a bo
    > for mapping user pages was the far better solution.
    > -Chris
    >
    > --
    > Chris Wilson, Intel Open Source Technology Centre
    >

    What kind of usage didn't played well with synchronous upload/download ? X, GL ?

    Cheers,
    Jerome


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