[Bug 102260] 15% perf drop in DrvRes with "i965/miptree: Use num_samples of 1 instead of 0 for single-sampled"

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=102260

            Bug ID: 102260
           Summary: 15% perf drop in DrvRes with "i965/miptree: Use
                    num_samples of 1 instead of 0 for single-sampled"
           Product: Mesa
           Version: git
          Hardware: Other
                OS: All
            Status: NEW
          Severity: normal
          Priority: medium
         Component: Drivers/DRI/i965
          Assignee: intel-3d-bugs at lists.freedesktop.org
          Reporter: eero.t.tamminen at intel.com
        QA Contact: intel-3d-bugs at lists.freedesktop.org

Bisecting on SKL GT2 revealed following commit:
----------------------------------------------------
commit 76e2f390f9863a356d1419982dec705260d67eff
Author:     Topi Pohjolainen <topi.pohjolainen at intel.com>
AuthorDate: Wed Jul 19 09:25:19 2017 +0300
Commit:     Topi Pohjolainen <topi.pohjolainen at intel.com>
CommitDate: Thu Jul 20 11:32:21 2017 +0300

    i965/miptree: Use num_samples of 1 instead of 0 for single-sampled
----------------------------------------------------

To be responsible for large performance drop in SynMark v7 DrvRes test.

Drop is largest (~15%) on SKL & KBL GT2, on most platforms it's 3-5%, on SKL
GT4e there's no measurable impact.

(Test is run in FullHD fullscreen.)

>From the commit message it seems that it should be just refactoring + potential
bug fix i.e. this large perf impact is unexpected.  Other tests beside DrvRes
weren't noticeably impacted.

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