Re: [PATCH v6] virtio_blk: add DISCARD and WRIET ZEROES commands support
From: Stefan Hajnoczi <stefanha@redhat.com>
Date: 2018-06-07 13:10:03
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 <redacted> --- CHANGELOG: v6: don't set T_OUT bit to discard and write zeroes commands.
I don't see this in the patch...
quoted hunk ↗ jump to hunk
@@ -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.