On 10/31/24 3:39 PM, Jens Axboe wrote: > On 10/31/24 3:24 PM, Jens Axboe wrote: >> On 10/25/24 6:22 AM, Ming Lei wrote: >>> SQE group is defined as one chain of SQEs starting with the first SQE that >>> has IOSQE_SQE_GROUP set, and ending with the first subsequent SQE that >>> doesn't have it set, and it is similar with chain of linked SQEs. >>> >>> Not like linked SQEs, each sqe is issued after the previous one is >>> completed. All SQEs in one group can be submitted in parallel. To simplify >>> the implementation from beginning, all members are queued after the leader >>> is completed, however, this way may be changed and leader and members may >>> be issued concurrently in future. >>> >>> The 1st SQE is group leader, and the other SQEs are group member. The whole >>> group share single IOSQE_IO_LINK and IOSQE_IO_DRAIN from group leader, and >>> the two flags can't be set for group members. For the sake of >>> simplicity, IORING_OP_LINK_TIMEOUT is disallowed for SQE group now. >>> >>> When the group is in one link chain, this group isn't submitted until the >>> previous SQE or group is completed. And the following SQE or group can't >>> be started if this group isn't completed. Failure from any group member will >>> fail the group leader, then the link chain can be terminated. >>> >>> When IOSQE_IO_DRAIN is set for group leader, all requests in this group and >>> previous requests submitted are drained. Given IOSQE_IO_DRAIN can be set for >>> group leader only, we respect IO_DRAIN by always completing group leader as >>> the last one in the group. Meantime it is natural to post leader's CQE >>> as the last one from application viewpoint. >>> >>> Working together with IOSQE_IO_LINK, SQE group provides flexible way to >>> support N:M dependency, such as: >>> >>> - group A is chained with group B together >>> - group A has N SQEs >>> - group B has M SQEs >>> >>> then M SQEs in group B depend on N SQEs in group A. >>> >>> N:M dependency can support some interesting use cases in efficient way: >>> >>> 1) read from multiple files, then write the read data into single file >>> >>> 2) read from single file, and write the read data into multiple files >>> >>> 3) write same data into multiple files, and read data from multiple files and >>> compare if correct data is written >>> >>> Also IOSQE_SQE_GROUP takes the last bit in sqe->flags, but we still can >>> extend sqe->flags with io_uring context flag, such as use __pad3 for >>> non-uring_cmd OPs and part of uring_cmd_flags for uring_cmd OP. >> >> Did you run the liburing tests with this? I rebased it on top of the >> flags2 patch I just sent out, and it fails defer-taskrun and crashes >> link_drain. Don't know if others fail too. I'll try the original one >> too, but nothing between those two should make a difference. It passes >> just fine with just the flags2 patch, so I'm a bit suspicious this patch >> is the issue. > > False alarm, it was my messup adding the group flag. Works just fine. > I'm attaching the version I tested, on top of that flags2 patch. > > Since we're on the topic - my original bundle patch used a bundle OP to > define an sqe grouping, which didn't need to use an sqe flag. Any > particular reason why you went with a flag for this one? > > I do think it comes out nicer with a flag for certain things, like being > able to link groups. Maybe that's the primary reason. Various hickups, please just see the patches here, works now: https://git.kernel.dk/cgit/linux/log/?h=io_uring-group -- Jens Axboe
