[Bug 107426] i915 kernel driver unable to initialize device (-28) ( Xeon E3-1275 v6 ) unless Aperture size <= 128MB

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=107426

--- Comment #16 from Chris Wilson <chris at chris-wilson.co.uk> ---
(In reply to Krist from comment #14)
> Created attachment 140891 [details]
> 256MB: lspci -vvv -s 0:0:2

Ok, we are not going completely mad, your BIOS is buggy.

(In reply to Krist from comment #15)
> The mappable limit of 128MB is affecting us, because we are trying to run 4
> different HD video encoders using the Intel Media SDK.
> For running all these video encoders, we are required to have numerous VA
> Surface buffers and we need more than 128MB of them.

Mappable has no impact on the amount of usable memory. It impacts the number of
surfaces that can be directly mapped through the very slow indirect GTT. If
userspace is using that as it's preferred means of access, it needs to be
shouted at. Still, that is handled as 2MiB chunks, the size of surface and the
number of them have little impact, the size of the aperture basically means how
many concurrent access you can handle before thrashing forces eviction.

The biggest consume of mappable is the display engine, but even that can handle
unmmappable memory for the main part (some features like FBC not withstanding).

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