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    SubjectRe: [PATCH] drm/i915,agp/intel: Do not clear stolen entries
    > On Jan 30, 2011, at 1:28 AM, Hugh Dickins wrote:
    > > I just tried setting the debug to 7 for a few seconds on 2.6.37, where
    > > I see no problem: I appear to get the "pipe a underrun" messages with
    > > that too; and the drm_ioctl messages, but much much fewer of them.
    > > Though I've been veering between i386 and x86_64 in these tests, so
    > > keep that in mind if what I'm saying makes no sense: the huge number
    > > of drm_ioctls was with 2.6.36-rc2 (plus some of Chris's fixes) on
    > > i386; the 64 underruns per second was with 2.6.36-rc2 (plus some of

    There shouldn't be any difference between the drm_ioctl() calls between
    2.6.37 and 2.6.38 as the userspace is the same. I think this might the
    crux of the issue. Can you attach a drm.debug=0xe boot dmesg, and a sample
    of drm.debug=0x7 during the busy period for .37 and .38? And also your

    Running fvwm and a couple of xterms you should not be utilizing vblanks at
    all (not even suffering the vblank interrupt being enabled) so this code
    should not even be causing unwanted side-effects. Bizarre.

    The delay in characters showing up is a bug in the ddx; the render queue
    is not being flushed before X goes to sleep. It's either the batch not
    being submitted or the render cache not being flushed to the scan out in a
    timely manner. (And these bugs can be complicated further by the
    introduction of a compositing WM.) Both bugs have existed off-and-on in
    the ddx over the years. And over time, we have weaned the kernel from
    flushing the graphics caches unnecessarily; though the larger impact would
    have been during the .37 cycle, at least the ones that sprang to mind as
    likely candidates.

    The pipe-a underrun is a nuisance; at best nothing will happen, there's an
    outside chance that your display may flicker and at worst your machine may
    hard hang.

    Chris Wilson, Intel Open Source Technology Centre

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