On 1/25/24 00:41, Keith Busch wrote: > On Wed, Jan 24, 2024 at 07:59:54PM +0800, Ming Lei wrote: >> Requests are added to plug list in reverse order, and both virtio-blk >> and nvme retrieves request from plug list in order, so finally requests >> are submitted to hardware in reverse order via nvme_queue_rqs() or >> virtio_queue_rqs, see: >> >> io_uring submit_bio vdb 6302096 4096 >> io_uring submit_bio vdb 12235072 4096 >> io_uring submit_bio vdb 7682280 4096 >> io_uring submit_bio vdb 11912464 4096 >> io_uring virtio_queue_rqs vdb 11912464 4096 >> io_uring virtio_queue_rqs vdb 7682280 4096 >> io_uring virtio_queue_rqs vdb 12235072 4096 >> io_uring virtio_queue_rqs vdb 6302096 4096 >> >> >> May this reorder be one problem for virtio-blk and nvme-pci? > > For nvme, it depends. Usually it's probably not a problem, though some > pci ssd's have optimizations for sequential IO that might not work if > these get reordered. ZNS and zoned virtio-blk drives... Cannot use io_uring at the moment. But I do not thing we reliably can anyway, unless the issuer is CPU/ring aware and always issue writes to a zone using the same ring. -- Damien Le Moal Western Digital Research
