On Wed, Jun 06, 2018 at 12:19:00PM +0800, Changpeng Liu wrote: > Existing virtio-blk protocol doesn't have DISCARD/WRITE ZEROES commands > support, this will impact the performance when using SSD backend over > file systems. > > Commit 88c85538 "virtio-blk: add discard and write zeroes features to > specification"(see https://github.com/oasis-tcs/virtio-spec) extended > existing virtio-blk protocol, adding extra DISCARD and WRITE ZEROES > commands support. > > While here, using 16 bytes descriptor to describe one segment of DISCARD > or WRITE ZEROES commands, each command may contain one or more decriptors. > > The following data structure shows the definition of one descriptor: > > struct virtio_blk_discard_write_zeroes { > le64 sector; > le32 num_sectors; > le32 unmap; > }; > > Field 'sector' means the start sector for DISCARD and WRITE ZEROES, > filed 'num_sectors' means the number of sectors for DISCARD and WRITE > ZEROES, if both DISCARD and WRITE ZEROES are supported, field 'unmap' > maybe used for WRITE ZEROES command with DISCARD enabled. > > We also extended the virtio-blk configuration space to let backend > device put DISCARD and WRITE ZEROES configuration parameters. > > struct virtio_blk_config { > [...] > > le32 max_discard_sectors; > le32 max_discard_seg; > le32 discard_sector_alignment; > le32 max_write_zeroes_sectors; > le32 max_write_zeroes_seg; > u8 write_zeroes_may_unmap; > } > > New feature bit [VIRTIO_BLK_F_DISCARD (13)]: Device can support discard > command, maximum discard sectors size in field 'max_discard_sectors' and > maximum discard segment number in field 'max_discard_seg'. > > New feature [VIRTIO_BLK_F_WRITE_ZEROES (14)]: Device can support write > zeroes command, maximum write zeroes sectors size in field > 'max_write_zeroes_sectors' and maximum write zeroes segment number in > field 'max_write_zeroes_seg'. > > The parameters in the configuration space of the device field > 'max_discard_sectors' and field 'discard_sector_alignment' are expressed in > 512-byte units if the VIRTIO_BLK_F_DISCARD feature bit is negotiated. The > field 'max_write_zeroes_sectors' is expressed in 512-byte units if the > VIRTIO_BLK_F_WRITE_ZEROES feature bit is negotiated. > > Signed-off-by: Changpeng Liu <changpeng.liu@xxxxxxxxx> > --- > CHANGELOG: > v6: don't set T_OUT bit to discard and write zeroes commands. I don't see this in the patch... > @@ -225,6 +260,7 @@ static blk_status_t virtio_queue_rq(struct blk_mq_hw_ctx *hctx, > int qid = hctx->queue_num; > int err; > bool notify = false; > + bool unmap = false; > u32 type; > > BUG_ON(req->nr_phys_segments + 2 > vblk->sg_elems); > @@ -237,6 +273,13 @@ static blk_status_t virtio_queue_rq(struct blk_mq_hw_ctx *hctx, > case REQ_OP_FLUSH: > type = VIRTIO_BLK_T_FLUSH; > break; > + case REQ_OP_DISCARD: > + type = VIRTIO_BLK_T_DISCARD; > + break; > + case REQ_OP_WRITE_ZEROES: > + type = VIRTIO_BLK_T_WRITE_ZEROES; > + unmap = !(req->cmd_flags & REQ_NOUNMAP); > + break; > case REQ_OP_SCSI_IN: > case REQ_OP_SCSI_OUT: > type = VIRTIO_BLK_T_SCSI_CMD; > @@ -256,6 +299,12 @@ static blk_status_t virtio_queue_rq(struct blk_mq_hw_ctx *hctx, > > blk_mq_start_request(req); > > + if (type == VIRTIO_BLK_T_DISCARD || type == VIRTIO_BLK_T_WRITE_ZEROES) { > + err = virtblk_setup_discard_write_zeroes(req, unmap); > + if (err) > + return BLK_STS_RESOURCE; > + } > + > num = blk_rq_map_sg(hctx->queue, req, vbr->sg); > if (num) { > if (rq_data_dir(req) == WRITE) ...since we still do blk_rq_map_sg() here and num should be != 0.
Attachment:
signature.asc
Description: PGP signature
_______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization
