xsk: fix immature cq descriptor production #9617
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Eryk reported an issue that I have put under Closes: tag, related to umem addrs being prematurely produced onto pool's completion queue. Let us make the skb's destructor responsible for producing all addrs that given skb used. Commit from fixes tag introduced the buggy behavior, it was not broken from day 1, but rather when XSK multi-buffer got introduced. In order to mitigate performance impact as much as possible, mimic the linear and frag parts within skb by storing the first address from XSK descriptor at sk_buff::destructor_arg. For fragments, store them at ::cb via list. The nodes that will go onto list will be allocated via kmem_cache. xsk_destruct_skb() will consume address stored at ::destructor_arg and optionally go through list from ::cb, if count of descriptors associated with this particular skb is bigger than 1. Previous approach where whole array for storing UMEM addresses from XSK descriptors was pre-allocated during first fragment processing yielded too big performance regression for 64b traffic. In current approach impact is much reduced on my tests and for jumbo frames I observed traffic being slower by at most 9%. Magnus suggested to have this way of processing special cased for XDP_SHARED_UMEM, so we would identify this during bind and set different hooks for 'backpressure mechanism' on CQ and for skb destructor, but given that results looked promising on my side I decided to have a single data path for XSK generic Tx. I suppose other auxiliary stuff such as helpers introduced in this patch would have to land as well in order to make it work, so we might have ended up with more noisy diff. Fixes: b7f72a3 ("xsk: introduce wrappers and helpers for supporting multi-buffer in Tx path") Reported-by: Eryk Kubanski <[email protected]> Closes: https://lore.kernel.org/netdev/[email protected]/ Signed-off-by: Maciej Fijalkowski <[email protected]>
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Pull request for series with
subject: xsk: fix immature cq descriptor production
version: 7
url: https://patchwork.kernel.org/project/netdevbpf/list/?series=997014