Re: [LSF/MM/BPF TOPIC] dmabuf backed read/write

[Pavel Begunkov <asml.silence@gmail.com>]

On 2/3/26 18:07, Keith Busch wrote:
> On Tue, Feb 03, 2026 at 02:29:55PM +0000, Pavel Begunkov wrote:
>> Good day everyone,
>>
...
>> Tushar was helping and mention he got good numbers for P2P transfers
>> compared to bouncing it via RAM. Anuj, Kanchan and Nitesh also
>> previously reported encouraging results for system memory backed
>> dma-buf for optimising IOMMU overhead, quoting Anuj:
>>
>> - STRICT: before = 570 KIOPS, after = 5.01 MIOPS
>> - LAZY: before = 1.93 MIOPS, after = 5.01 MIOPS
>> - PASSTHROUGH: before = 5.01 MIOPS, after = 5.01 MIOPS
> 
> Thanks for submitting the topic. The performance wins look great, but
> I'm a little surpised passthrough didn't show any difference. We're
> still skipping a bit of transformations with the dmabuf compared to not
> having it, so maybe it's just a matter of crafting the right benchmark
> to show the benefit.

My first thought was that hardware couldn't push more and would
be great to have idle numbers, but Anuj already demystified it.

> Anyway, I look forward to the next version of this feature. I promise to
> have more cycles to review and test the v3.

Thanks! And in general, IMHO at this point waiting for next
version would be more time efficient for reviewers.

-- 
Pavel Begunkov