On 10/10/2024 21:35, David Wei wrote:
On 2024-10-09 11:21, Pedro Tammela wrote:
On 09/10/2024 13:55, Mina Almasry wrote:
[...]
If not, I would like to see a comparison between TCP RX zerocopy and
this new io-uring zerocopy. For Google for example we use the TCP RX
zerocopy, I would like to see perf numbers possibly motivating us to
move to this new thing.
[1] https://lwn.net/Articles/752046/
Hi!
From my own testing, the TCP RX Zerocopy is quite heavy on the page unmapping side. Since the io_uring implementation is expected to be lighter (see patch 11), I would expect a simple comparison to show better numbers for io_uring.
Hi Pedro, I will add TCP_ZEROCOPY_RECEIVE to kperf and compare in the
next patchset.
To be fair to the existing implementation, it would then be needed to be paired with some 'real' computation, but that varies a lot. As we presented in netdevconf this year, HW-GRO eventually was the best option for us (no app changes, etc...) but still a case by case decision.
Why is there a need to add some computation to the benchmarks? A
benchmark is meant to be just that - a simple comparison that just looks
at the overheads of the stack.
For the use case we saw, streaming lots of data with zc, the RX pages
would linger for a reasonable time
in processing and the unmap cost amortized in the hotpath.
Which was not considered in our simple benchmark.
So for Mina's case, I guess the only way to know for sure if it's worth
is to implement the io_uring approach and compare.
Real workloads are complex, I don't see> this feature as a universal win in all cases, but very workload and
userspace architecture dependent.
100% agree here, that's our experience so far as well.
Just wanted to share this sentiment in my previous email.
I personally believe the io_uring approach will encompass more use cases
than the existing implementation.
As for HW-GRO, whynotboth.jpg?
For us the cost of changing the apps/services to accomodate rx zc was
prohibitive for now,
which lead us to stick with HW-GRO.
IIRC, you mentioned in netdevconf Meta uses a library for RPC, but we
don't have this luxury :/
