[Intel-gfx] [PATCH 0/6] Page faults to help user space debug

[Daniel Vetter]

On Sat, Jun 29, 2013 at 02:20:40PM -0700, Ben Widawsky wrote:
> On Sat, Jun 29, 2013 at 04:38:00PM +0200, Daniel Vetter wrote:
> > On Sat, Jun 29, 2013 at 12:23 AM, Ben Widawsky <ben at bwidawsk.net> wrote:
> > > 2. echo 2 > /sys/kernel/debug/dri/0/i915_debug_flags
> > > Unbind all buffers synchronously, so any batch which has bad code will fault
> > > every time and not get lucky by hitting a buffer it bound. This will not catch
> > > cases where it accidentally reads/writes someone else's buffer.
> > 
> > We already have this as the drop_caches debugfs interface. Chris used
> > it to reproduce the 3.7 reloc-tree regression, the only downside is
> > that no one ever got around to write the respective i-g-t ... :(
> > -Daniel
> 
> In order to achieve the same behavior, one must instrument every GPU
> client to use that interface before, and after every batch (you can skip
> one if you're positive all clients have opted in). Also, every client
> must be run as root.
> 
> This mechanism I've introduced is much simpler to achieve the intended
> result.

Oh right, your patch is doing something else completely. One thing which
would be neat on top of this is to randomize the locations of each bo a
bit (varibale padding in front should be good enough). That way we can
check whether the relocations are all handled properly.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch