Re: [PATCH v2 RESEND 4/7] swiotlb: Dynamically allocated bounce buffers

[Petr Tesařík]

On Wed, 17 May 2023 08:35:10 +0200
Petr Tesařík <petr@xxxxxxxxxxx> wrote:

>[...]
> Anyway, my greatest objection to allocating additional swiotlb chunks is
> that _all_ of them must be searched to determine that the physical
> address does _not_ belong to a swiotlb, incurring performance penalty

I thought about this part again, and I overlooked one option. We can
track only the _active_ swiotlbs for each device. If a device never
needs a swiotlb, there is no active swiotlb, and is_swiotlb_buffer()
short-circuits to false. This should avoid all collateral damage to
innocent devices.

We would also maintain a (global) list of all allocated swiotlbs, used
by swiotlb_map() to find free slots and add the respective swiotlb to
the per-device active list.

One potential advantage is that we could use mapping size and alignment
to choose a swiotlb cleverly and minimize internal fragmentation...

OK, I'm dreaming. Let's agree on the general approach first.

Petr T