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
