Once we thought we got semaphores working, we disabled kicking the ring
if hangcheck fired whilst waiting upon a ring as it was doing more harm
than good:
commit 4e0e90dcb8
Author: Daniel Vetter <daniel.vetter@ffwll.ch>
Date: Wed Dec 14 13:56:58 2011 +0100
drm/i915: kicking rings stuck on semaphores considered harmful
However, life is never that easy and semaphores are still causing
problems whereby the value written by one ring (bcs) is not being
propagated to the waiter (rcs). Thus the waiter never wakes up and we
declare the GPU hung, which often has unfortunate consequences, even if
we successfully reset the GPU.
But the GPU is idle as it has completed the work, just didn't notify its
clients. So we can detect the incomplete wait during hang check and
probe the target ring to see if has indeed emitted the breadcrumb seqno
following the work and then and only then kick the waiter.
Based on a suggestion by Ben Widawsky.
v2: cross-check wait with iphdr. fix signaller calculation.
References: https://bugs.freedesktop.org/show_bug.cgi?id=54226
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Mika Kuoppala <mika.kuoppala@intel.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Ben Widawsky <ben@bwidawsk.net>
Acked-by: Ben Widawsky <ben@bwidawsk.net>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
************************************************************
* For the very latest on DRI development, please see: *
* http://dri.freedesktop.org/ *
************************************************************
The Direct Rendering Manager (drm) is a device-independent kernel-level
device driver that provides support for the XFree86 Direct Rendering
Infrastructure (DRI).
The DRM supports the Direct Rendering Infrastructure (DRI) in four major
ways:
1. The DRM provides synchronized access to the graphics hardware via
the use of an optimized two-tiered lock.
2. The DRM enforces the DRI security policy for access to the graphics
hardware by only allowing authenticated X11 clients access to
restricted regions of memory.
3. The DRM provides a generic DMA engine, complete with multiple
queues and the ability to detect the need for an OpenGL context
switch.
4. The DRM is extensible via the use of small device-specific modules
that rely extensively on the API exported by the DRM module.
Documentation on the DRI is available from:
http://dri.freedesktop.org/wiki/Documentation
http://sourceforge.net/project/showfiles.php?group_id=387
http://dri.sourceforge.net/doc/
For specific information about kernel-level support, see:
The Direct Rendering Manager, Kernel Support for the Direct Rendering
Infrastructure
http://dri.sourceforge.net/doc/drm_low_level.html
Hardware Locking for the Direct Rendering Infrastructure
http://dri.sourceforge.net/doc/hardware_locking_low_level.html
A Security Analysis of the Direct Rendering Infrastructure
http://dri.sourceforge.net/doc/security_low_level.html
a24a11e6b4