[Bug 108712] New: Kernel code no longer counts EU correctly for i5-5250U (HD Graphics 6000 BroadWell U-Processor GT3)

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=108712

            Bug ID: 108712
           Summary: Kernel code no longer counts EU correctly for i5-5250U
                    (HD Graphics 6000 BroadWell U-Processor GT3)
           Product: DRI
           Version: unspecified
          Hardware: x86-64 (AMD64)
                OS: Linux (All)
            Status: NEW
          Severity: normal
          Priority: medium
         Component: DRM/Intel
          Assignee: intel-gfx-bugs at lists.freedesktop.org
          Reporter: gordon.lack at dsl.pipex.com
        QA Contact: intel-gfx-bugs at lists.freedesktop.org
                CC: intel-gfx-bugs at lists.freedesktop.org

Created attachment 142439
  --> https://bugs.freedesktop.org/attachment.cgi?id=142439&action=edit
Attached information files, as noted n Description/Comment.

The Ubuntu Bioinc kernels (4.15.x) report an i5-5250U processor (with HD
Graphics 6000 BroadWell U-Processor GT3 GPU) as having 48 EUs.

The Cosmic ones (4.18.x) report it has having only 24. This is a result of only
4 EUs per sub-slice being counted (it should have 8). Unsurprisingly this
result sin a significant loss of compute power when software uses this value to
determine how to run.

The code that determines how many EUs there are is in intel_device_info.c, and
this was changed in the 4.17 kernel series by this commit:

https://github.com/torvalds/linux/commit/8cc7669355136f8952779e6f60053c1284d59c4d

I've attached the intel_reg dump info for the graphics set-up and also 4.15.x
and 4.18.x clinfo and the contents of the debug file-system
(/sys/kernel/debug/dri/0).
The clinfo output contains a debug statement added to the beignet code on the
system which reports what it gets from the register-reading kernel code, then
sets it to 48 regardless). This was originally reported as a beignet bug
(https://bugs.launchpad.net/ubuntu/+source/beignet/+bug/1800752).

Attachment files are:
   intel_reg_dump.txt
   4.15.0-38-generic.clinfo
   4.15.0-38-generic.dri-debug
   4.18.0-10-generic.clinfo
   4.18.0-10-generic.dri-debug

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