Re: [PATCH v4 0/8] Allow dynamic allocation of software IO TLB bounce buffers

[Petr Tesařík <petr@xxxxxxxxxxx>]

On Thu, 20 Jul 2023 08:52:16 +0200
Christoph Hellwig <hch@xxxxxx> wrote:

> Just to add a highlevel comment here after I feel like I need a little
> more time to review the guts.
> 
> I'm still pretty concerned about the extra list that needs to be
> consulted in is_swiotlb_buffer, but I can't really think of
> anything better.  Maybe an xarray has better cache characteristics,
> but that one requires even more allocations in the low-level dma map
> path.
> 
> One thing I'd like to see for the next version is to make the
> new growing code a config option at least for now.  It is a pretty
> big change of the existing swiotlb behavior, and I want people to opt
> into it conciously.  Maybe we can drop the option again after a few
> years once everything has settled.

Fine with me. I removed it after all my testing showed no performance
impact as long as the size of the initial SWIOTLB is kept at the
default value (and sufficient for the workload), but it's OK for me if
dynamic SWIOTLB allocations are off by default.

OTOH I'd like to make it a boot-time option rather than build-time
option. Would that be OK for you?

Petr T