Re: [LSF/MM/BPF ATTEND][LSF/MM/BPF Topic] Non-block IO

[John Garry <john.g.garry@oracle.com>]

On 10/02/2023 18:18, Bart Van Assche wrote:
> On 2/10/23 10:00, Kanchan Joshi wrote:
>> 3. DMA cost: is high in presence of IOMMU. Keith posted the work[1],
>> with block IO path, last year. I imagine plumbing to get a bit simpler
>> with passthrough-only support. But what are the other things that must
>> be sorted out to have progress on moving DMA cost out of the fast path?
> 
> Are performance numbers available?
> 
> Isn't IOMMU cost something that has already been solved? From 
> https://www.usenix.org/system/files/conference/atc15/atc15-paper-peleg.pdf: "Evaluation of our designs under Linux shows that (1)
> they achieve 88.5%–100% of the performance obtained
> without an IOMMU".

That paper is ~8 years old now. Some recommendations are already 
supported in the kernel since then, like per-CPU IOVA caching and 
per-IOMMU domain IOTLB flushing with per-CPU queues (which is relevant 
to lazy mode only).

Thanks,
John