[Intel-gfx] Regression since 53984635a659e360f206a81ada4ae813152d72f1 (drm/i915: use the complete gtt)

[Peter Clifton]

commit 53984635a659e360f206a81ada4ae813152d72f1
Author: Daniel Vetter <daniel.vetter at ffwll.ch>
Date:   Wed Sep 22 23:44:24 2010 +0200

    drm/i915: use the complete gtt
    
    At least the part that's currently enabled by the BIOS.
    
    Signed-off-by: Daniel Vetter <daniel.vetter at ffwll.ch>
    Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>


Since the above commit, my GL app will crash after a period of sustained
graphics activity. It appears to use quite a lot of small BOs for
uploading changed VBO data with glBufferSubData, and I don't think these
are being purged until the GTT is full.

For some reason, with gtt size != mappable size, the GPU will hang after
a while. I had thought that we were missing a guard page from
mappable_size, but subtracting a PAGE_SIZE did not help. Only resetting
gtt_size to mappable_size (still subtracting a guard page) helped.

Adding some instrumentation shows:

Prealloc size 33550336, gtt size 2147479552, mappable size 268435456

This is an GM45 on a HP 6730b laptop.

Any hints as to where to look now?

Are things being put into unmappable GTT space when they need to be
mappable? Is purging all my purgable BOs taking too long and causing a
HANG to be declared? (NB: Hang still occurs if I increase hangcheck
timer to over a second).

Best regards,

-- 
Peter Clifton

Electrical Engineering Division,
Engineering Department,
University of Cambridge,
9, JJ Thomson Avenue,
Cambridge
CB3 0FA

Tel: +44 (0)7729 980173 - (No signal in the lab!)
Tel: +44 (0)1223 748328 - (Shared lab phone, ask for me)