Re: [PATCH v6] swiotlb: Adjust SWIOTBL bounce buffer size for SEV guests.

[Borislav Petkov]

On Tue, Nov 24, 2020 at 09:25:06AM +0000, Kalra, Ashish wrote:
> But what will be the criteria to figure out this percentage?
>
> As I mentioned earlier, this can be made as complicated as possible by
> adding all kind of heuristics but without any predictable performance
> gain.
>
> Or it can be kept simple by using a static percentage value.

Yes, static percentage number based on the guest memory. X% of the guest
memory is used for SWIOTLB.

Since you use sev_active(), it means the size computation is done in the
guest so that SWIOTLB size is per-guest. Yes?

If so, you can simply take, say, 5% of the guest memory's size and use
that for SWIOTLB buffers. Or 6 or X or whatever.

Makes sense?

-- 
Regards/Gruss,
    Boris.

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