Re: Large CQE for fuse headers

[Jens Axboe <axboe@kernel.dk>]

On 10/10/24 2:56 PM, Bernd Schubert wrote:
> Hello,
> 
> as discussed during LPC, we would like to have large CQE sizes, at least
> 256B. Ideally 256B for fuse, but CQE512 might be a bit too much...
> 
> Pavel said that this should be ok, but it would be better to have the CQE
> size as function argument. 
> Could you give me some hints how this should look like and especially how
> we are going to communicate the CQE size to the kernel? I guess just adding
> IORING_SETUP_CQE256 / IORING_SETUP_CQE512 would be much easier.

Not Pavel and unfortunately I could not be at that LPC discussion, but
yeah I don't see why not just adding the necessary SETUP arg for this
would not be the way to go. As long as they are power-of-2, then all
it'll impact on both the kernel and liburing side is what size shift to
use when iterating CQEs.

Since this obviously means larger CQ rings, one nice side effect is that
since 6.10 we don't need contig pages to map any of the rings. So should
work just fine regardless of memory fragmentation, where previously that
would've been a concern.

-- 
Jens Axboe