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Date: Tue, 18 Oct 2022 10:43:17 +0200 From: Stefan Metzmacher <metze@...ba.org> To: Pavel Begunkov <asml.silence@...il.com>, io-uring <io-uring@...r.kernel.org>, Jens Axboe <axboe@...nel.dk> Cc: Jakub Kicinski <kuba@...nel.org>, netdev <netdev@...r.kernel.org>, Dylan Yudaken <dylany@...com> Subject: Re: IORING_CQE_F_COPIED Hi Pavel, > On 10/14/22 12:06, Stefan Metzmacher wrote: >> Hi Pavel, >> >> In the tests I made I used this version of IORING_CQE_F_COPIED: >> https://git.samba.org/?p=metze/linux/wip.git;a=commitdiff;h=645d3b584c417a247d92d71baa6266a5f3d0d17d >> (also inlined at the end) >> >> Would that something we want for 6.1? (Should I post that with a useful commit message, after doing some more tests) > > I was thinking, can it be delivered separately but not in the same cqe? > The intention is to keep it off the IO path. For example, it can emit a > zc status CQE or maybe keep a "zc failed" counter inside the ring. Other > options? And we can add a separate callback for that, will make a couple > of things better. > > What do you think? Especially from the userspace usability perspective. So far I can't think of any other way that would be useful yet, but that doesn't mean something else might exist... IORING_CQE_F_COPIED is available per request and makes it possible to judge why the related SENDMSG_ZC was fast or not. It's also available in trace-cmd report. Everything else would likely re-introduce similar complexity like we had with the notif slots. Instead of a new IORING_CQE_F_COPIED flag we could also set cqe.res = SO_EE_CODE_ZEROCOPY_COPIED, but that isn't really different. As I basically use the same logic that's used to generate SO_EE_CODE_ZEROCOPY_COPIED for the native MSG_ZEROCOPY, I don't see the problem with IORING_CQE_F_COPIED. Can you be more verbose why you're thinking about something different? metze
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