[Bug 92975] [SKL][v4.3 bisected]SKL OpenCL performance reduced hugely

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=92975

Jani Nikula <jani.nikula at intel.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |NEEDINFO

--- Comment #4 from Jani Nikula <jani.nikula at intel.com> ---
(In reply to meng from comment #2)
> No "i915.preliminary_hw_support=1" set in grub.

Before v4.3 you don't get SKL gfx support without that, or
CONFIG_DRM_I915_PRELIMINARY_HW_SUPPORT=y.

When running pre-v4.3, do you see something along these lines in the dmesg:

"""
This hardware requires preliminary hardware support.
See CONFIG_DRM_I915_PRELIMINARY_HW_SUPPORT, and/or modparam
preliminary_hw_support
"""

> By skipping many commits, found out the first bad commit:
> commit 3bbaba0ceaa254c9ee261e329bfd92e4ba4fe32a
> Author: Peter Antoine <peter.antoine at intel.com>
> Date:   Fri Jul 10 20:13:11 2015 +0300
> 
>     drm/i915: Added Programming of the MOCS

Please pick a badly performing kernel (verify that it does!) and then try this
on top:

diff --git a/drivers/gpu/drm/i915/intel_lrc.c
b/drivers/gpu/drm/i915/intel_lrc.c
index 06180dce954e..0eaeccdc5a49 100644
--- a/drivers/gpu/drm/i915/intel_lrc.c
+++ b/drivers/gpu/drm/i915/intel_lrc.c
@@ -1867,7 +1867,7 @@ static int gen8_init_rcs_context(struct
drm_i915_gem_request *req)
     if (ret)
         return ret;

-    ret = intel_rcs_context_init_mocs(req);
+    ret = 1;
     /*
      * Failing to program the MOCS is non-fatal.The system will not
      * run at peak performance. So generate an error and carry on.

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