8cd999181f
On Braswell, under heavy stress, if we update the GGTT while
simultaneously accessing another region inside the GTT, we are returned
the wrong values. To prevent this we stop the machine to update the GGTT
entries so that no memory traffic can occur at the same time.
This was first spotted in
commit 5bab6f60cb4d1417ad7c599166bcfec87529c1a2
Author: Chris Wilson <chris@chris-wilson.co.uk>
Date: Fri Oct 23 18:43:32 2015 +0100
drm/i915: Serialise updates to GGTT with access through GGTT on Braswell
but removed again in forlorn hope with
commit 4509276ee824bb967885c095c610767e42345c36
Author: Chris Wilson <chris@chris-wilson.co.uk>
Date: Mon Feb 20 12:47:18 2017 +0000
drm/i915: Remove Braswell GGTT update w/a
However, gem_concurrent_blit is once again only stable with the patch
applied and CI is detecting the odd failure in forked gem_mmap_gtt tests
(which smell like the same issue). Fwiw, a wide variety of CPU memory
barriers (around GGTT flushing, fence updates, PTE updates) and GPU
flushes/invalidates (between requests, after PTE updates) were tried as
part of the investigation to find an alternate cause, nothing comes
close to serialised GGTT updates.
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=105591
Testcase: igt/gem_concurrent_blit
Testcase: igt/gem_mmap_gtt/*forked*
References: 5bab6f60cb4d ("drm/i915: Serialise updates to GGTT with access through GGTT on Braswell")
References: 4509276ee824 ("drm/i915: Remove Braswell GGTT update w/a")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190114211729.30352-1-chris@chris-wilson.co.uk
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.