[Bug 111731] [SKL GT4e] large perf drop (up to 27%) in most 3D benchmarks

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=111731

--- Comment #4 from Eero Tamminen <eero.t.tamminen at intel.com> ---
(In reply to Chris Wilson from comment #3)
> > (Why IOMMU perf impact would be SKL GT4e specific?)
> 
> My guess at this moment would be that eDRAM feels the hit more
> significantly. Or that we've just got the caching completely wrong on that
> sku.

We were supposed to have VT-d disabled from BIOS in all our machines, but
apparently that had been enabled when SkullCanyon was in other use for a while.
I.e. it was only machine with VT-d enabled.


> 20+% regression is also in line with some kbl (gt3e iirc) media runs I did.

Media, not 3D?  (That's more than I saw on SkullCanyon in media test-cases.)

I've now enabled VT-d on few other machines (BDW GT2, BXT, SKL GT2, KBL GT3e)
to get you a bit more perf info.  I'll add that info here later this week.

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