> But you said without the fix it doesn't work at all?  Or is this
> the same box, just with the aic7xxx controller disabled?
>
> In general the patch should only have two effects:
>
>  - set a small amount of memory aside for bounce buffering
>  - switch the default dma_ops from dma_direct_ops to swiotlb_ops
>
> I can't really see how either could have such a huge effect, even with
> swiotlb having a couple more wired up ops for which we'd enable spectre
> mitigations.
>
> So a strict before and after would be very interesting, if it is really
> just this one change that causes such a huge drop we have hidden dragons
> somewhere..

Christoph,
  I did a very controlled before-and-after and got very sensible
results. All compiles were close in time with patched and un-patched
kernels.

I must have screwed something up with my last round of testing.

Ingo: I am confident this patch should be accepted.

- Matthew Whitehead
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