On Sun, Aug 15, 2021 at 04:12:04PM +0200, Pablo Neira Ayuso wrote: > On Sun, Aug 15, 2021 at 03:32:30PM +0200, alexandre.ferrieux@xxxxxxxxxx wrote: > > On 8/15/21 3:07 PM, Pablo Neira Ayuso wrote: > > > On Sun, Aug 15, 2021 at 02:17:08PM +0200, alexandre.ferrieux@xxxxxxxxxx wrote: > > > [...] > > > > So, the only way forward would be a separate hashtable on ids. > > > > > > Using the rhashtable implementation is fine for this, it's mostly > > > boilerplate code that is needed to use it and there are plenty of > > > examples in the kernel tree if you need a reference. > > > > Thanks, that's indeed pretty simple. I was just worried that people would > > object to adding even the slightest overhead (hash_add/hash_del) to the > > existing code path, that satisfies 99% of uses (LIFO). What do you think ? > > It should be possible to maintain both the list and the hashtable, > AFAICS, the batch callback still needs the queue_list. > > > > > PS: what is the intended dominant use case for batch verdicts ? > > > > > > Issuing a batch containing several packets helps to amortize the > > > cost of the syscall. > > > > Yes, but that could also be achieved by passing an array of ids. > > You mean, one single sendmsg() with several netlink messages, that > would also work to achieve a similar batching effect. sendmsg() can actually be slower. I gave up on a project to send verdicts using sendmsg() (especially with large mangled packets), because benchmarking showed: 1. on a 3YO laptop, no discernable difference. 2. On a 1YO Ryzen desktop, sendmsg() significantly slower. sendmsg() sent 3 or 4 buffers: 1. leading netlink message blocks; 2. the packet; 3. padding to 4 bytes (if required); last: trailing netlink message blocks. sendmsg() saved moving these data blocks into a single buffer. But it introduced the overhead of the kernel's having to validate 4 userland buffers instead of 1. A colleague suggested the Ryzen result is because of having 128-bit registers to move data. I guess that must be it. The spreadsheets from the tests are up on GitHub: https://github.com/duncan-roe/nfq6/blob/main/laptop_timings.ods https://github.com/duncan-roe/nfq6/blob/main/timings.ods Cheers ... Duncan.
