On 21/12/2019 20:01, Jens Axboe wrote: > On 12/21/19 9:48 AM, Pavel Begunkov wrote: >> On 21/12/2019 19:38, Jens Axboe wrote: >>> On 12/21/19 9:20 AM, Pavel Begunkov wrote: >>>> On 21/12/2019 19:15, Pavel Begunkov wrote: >>>>> Double account ctx->refs keeping number of taken refs in ctx. As >>>>> io_uring gets per-request ctx->refs during submission, while holding >>>>> ctx->uring_lock, this allows in most of the time to bypass >>>>> percpu_ref_get*() and its overhead. >>>> >>>> Jens, could you please benchmark with this one? Especially for offloaded QD1 >>>> case. I haven't got any difference for nops test and don't have a decent SSD >>>> at hands to test it myself. We could drop it, if there is no benefit. >>>> >>>> This rewrites that @extra_refs from the second one, so I left it for now. >>> >>> Sure, let me run a peak test, qd1 test, qd1+sqpoll test on >>> for-5.6/io_uring, same branch with 1-2, and same branch with 1-3. That >>> should give us a good comparison. One core used for all, and we're going >>> to be core speed bound for the performance in all cases on this setup. >>> So it'll be a good comparison. >>> >> Great, thanks! > > For some reason, not seeing much of a change between for-5.6/io_uring > and 1+2 and 1+2+3, it's about the same and results seem very stable. > For reference, top of profile with 1-3 applied looks like this: I see. I'll probably drop the last one, as it only complicates things. My apologies for misleading terminology. Read-only QD1 (submit and wait until the userspace completes it) obviously won't saturate a CPU. Writes probably wouldn't as well (though, depends on HW). And it would be better to say -- submit by one, complete in a bunch. Just curious, what you used for testing? Is it fio? > > + 3.92% io_uring [kernel.vmlinux] [k] blkdev_direct_IO > + 3.87% io_uring [kernel.vmlinux] [k] blk_mq_get_request > + 3.43% io_uring [kernel.vmlinux] [k] io_iopoll_getevents > + 3.03% io_uring [kernel.vmlinux] [k] __slab_free > + 2.87% io_uring io_uring [.] submitter_fn > + 2.79% io_uring [kernel.vmlinux] [k] io_submit_sqes > + 2.75% io_uring [kernel.vmlinux] [k] bio_alloc_bioset > + 2.70% io_uring [nvme_core] [k] nvme_setup_cmd > + 2.59% io_uring [kernel.vmlinux] [k] blk_mq_make_request > + 2.46% io_uring [kernel.vmlinux] [k] io_prep_rw > + 2.32% io_uring [kernel.vmlinux] [k] io_read > + 2.25% io_uring [kernel.vmlinux] [k] blk_mq_free_request > + 2.19% io_uring [kernel.vmlinux] [k] io_put_req > + 2.06% io_uring [kernel.vmlinux] [k] kmem_cache_alloc > + 2.01% io_uring [kernel.vmlinux] [k] generic_make_request_checks > + 1.90% io_uring [kernel.vmlinux] [k] __sbitmap_get_word > + 1.86% io_uring [kernel.vmlinux] [k] sbitmap_queue_clear > + 1.85% io_uring [kernel.vmlinux] [k] io_issue_sqe > > -- Pavel Begunkov
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