scsi: target: tcmu: Optimize queue_cmd_ring()

queue_cmd_ring() needs to check whether there is enough space in cmd ring
and data area for the cmd to queue.

Currently the sequence is:

 1) Calculate size the cmd will occupy on the ring based on estimation of
    needed iovs.

 2) Check whether there is enough space on the ring based on size from 1)

 3) Allocate buffers in data area.

 4) Calculate number of iovs the command really needs while copying
    incoming data (if any) to data area.

 5) Re-calculate real size of cmd on ring based on real number of iovs.

 6) Set up possible padding and cmd on the ring.

Step 1) must not underestimate the cmd size so use max possible number of
iovs for the given I/O data size. The resulting overestimation can be
really high so this sequence is not ideal. The earliest the real number of
iovs can be calculated is after data buffer allocation. Therefore rework
the code to implement the following sequence:

 A) Allocate buffers on data area and calculate number of necessary iovs
    during this.

 B) Calculate real size of cmd on ring based on number of iovs.

 C) Check whether there is enough space on the ring.

 D) Set up possible padding and cmd on the ring.

The new sequence enforces the split of new function tcmu_alloc_data_space()
from is_ring_space_avail(). Using this function, change queue_cmd_ring()
according to the new sequence.

Change routines called by tcmu_alloc_data_space() to allow calculating and
returning the iov count. Remove counting of iovs in scatter_data_area().

Link: https://lore.kernel.org/r/20200910155041.17654-3-bstroesser@ts.fujitsu.com
Acked-by: Mike Christie <michael.christie@oracle.com>
Signed-off-by: Bodo Stroesser <bstroesser@ts.fujitsu.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

1 files changed, 102 insertions, 82 deletions

diff --git a/drivers/target/target_core_user.c b/drivers/target/target_core_user.c
index 411172d772b4..e4813bf41ee0 100644
--- a/drivers/target/target_core_user.c
+++ b/drivers/target/target_core_user.c
@@ -493,15 +493,16 @@ static void tcmu_cmd_free_data(struct tcmu_cmd *tcmu_cmd, uint32_t len)
 		clear_bit(tcmu_cmd->dbi[i], udev->data_bitmap);
 }
 
-static inline bool tcmu_get_empty_block(struct tcmu_dev *udev,
-					struct tcmu_cmd *tcmu_cmd)
+static inline int tcmu_get_empty_block(struct tcmu_dev *udev,
+				       struct tcmu_cmd *tcmu_cmd,
+				       int prev_dbi, int *iov_cnt)
 {
 	struct page *page;
 	int ret, dbi;
 
 	dbi = find_first_zero_bit(udev->data_bitmap, udev->dbi_thresh);
 	if (dbi == udev->dbi_thresh)
-		return false;
+		return -1;
 
 	page = radix_tree_lookup(&udev->data_blocks, dbi);
 	if (!page) {
@@ -525,24 +526,30 @@ static inline bool tcmu_get_empty_block(struct tcmu_dev *udev,
 	set_bit(dbi, udev->data_bitmap);
 	tcmu_cmd_set_dbi(tcmu_cmd, dbi);
 
-	return true;
+	if (dbi != prev_dbi + 1)
+		*iov_cnt += 1;
+
+	return dbi;
 err_insert:
 	__free_page(page);
 err_alloc:
 	atomic_dec(&global_db_count);
-	return false;
+	return -1;
 }
 
-static bool tcmu_get_empty_blocks(struct tcmu_dev *udev,
-				  struct tcmu_cmd *tcmu_cmd)
+static int tcmu_get_empty_blocks(struct tcmu_dev *udev,
+				 struct tcmu_cmd *tcmu_cmd, int dbi_cnt)
 {
-	int i;
+	/* start value of dbi + 1 must not be a valid dbi */
+	int dbi = -2;
+	int i, iov_cnt = 0;
 
-	for (i = tcmu_cmd->dbi_cur; i < tcmu_cmd->dbi_cnt; i++) {
-		if (!tcmu_get_empty_block(udev, tcmu_cmd))
-			return false;
+	for (i = 0; i < dbi_cnt; i++) {
+		dbi = tcmu_get_empty_block(udev, tcmu_cmd, dbi, &iov_cnt);
+		if (dbi < 0)
+			return -1;
 	}
-	return true;
+	return iov_cnt;
 }
 
 static inline struct page *
@@ -639,13 +646,12 @@ static inline size_t head_to_end(size_t head, size_t size)
 	return size - head;
 }
 
-static inline void new_iov(struct iovec **iov, int *iov_cnt)
+static inline void new_iov(struct iovec **iov, bool first)
 {
 	struct iovec *iovec;
 
-	if (*iov_cnt != 0)
+	if (!first)
 		(*iov)++;
-	(*iov_cnt)++;
 
 	iovec = *iov;
 	memset(iovec, 0, sizeof(struct iovec));
@@ -668,8 +674,7 @@ static inline size_t iov_tail(struct iovec *iov)
 
 static void scatter_data_area(struct tcmu_dev *udev,
 	struct tcmu_cmd *tcmu_cmd, struct scatterlist *data_sg,
-	unsigned int data_nents, struct iovec **iov,
-	int *iov_cnt, bool copy_data)
+	unsigned int data_nents, struct iovec **iov, bool copy_data)
 {
 	int i, dbi;
 	int block_remaining = 0;
@@ -677,6 +682,7 @@ static void scatter_data_area(struct tcmu_dev *udev,
 	size_t copy_bytes, to_offset, offset;
 	struct scatterlist *sg;
 	struct page *page;
+	bool first = true;
 
 	for_each_sg(data_sg, sg, data_nents, i) {
 		int sg_remaining = sg->length;
@@ -707,8 +713,7 @@ static void scatter_data_area(struct tcmu_dev *udev,
 			 */
 			copy_bytes = min_t(size_t, sg_remaining,
 					block_remaining);
-			if (*iov_cnt != 0 &&
-			    to_offset == iov_tail(*iov)) {
+			if (!first && to_offset == iov_tail(*iov)) {
 				/*
 				 * Will append to the current iovec, because
 				 * the current block page is next to the
@@ -721,9 +726,10 @@ static void scatter_data_area(struct tcmu_dev *udev,
 				 * first time here or the current block page
 				 * is not next to the previous one.
 				 */
-				new_iov(iov, iov_cnt);
+				new_iov(iov, first);
 				(*iov)->iov_base = (void __user *)to_offset;
 				(*iov)->iov_len = copy_bytes;
+				first = false;
 			}
 
 			if (copy_data) {
@@ -815,13 +821,11 @@ static inline size_t spc_bitmap_free(unsigned long *bitmap, uint32_t thresh)
 }
 
 /*
- * We can't queue a command until we have space available on the cmd ring *and*
- * space available on the data area.
+ * We can't queue a command until we have space available on the cmd ring.
  *
  * Called with ring lock held.
  */
-static bool is_ring_space_avail(struct tcmu_dev *udev, struct tcmu_cmd *cmd,
-				size_t cmd_size)
+static bool is_ring_space_avail(struct tcmu_dev *udev, size_t cmd_size)
 {
 	struct tcmu_mailbox *mb = udev->mb_addr;
 	size_t space, cmd_needed;
@@ -846,9 +850,22 @@ static bool is_ring_space_avail(struct tcmu_dev *udev, struct tcmu_cmd *cmd,
 		       udev->cmdr_last_cleaned, udev->cmdr_size);
 		return false;
 	}
+	return true;
+}
+
+/*
+ * We have to allocate data buffers before we can queue a command.
+ * Returns -1 on error (not enough space) or number of needed iovs on success
+ *
+ * Called with ring lock held.
+ */
+static int tcmu_alloc_data_space(struct tcmu_dev *udev, struct tcmu_cmd *cmd,
+				  int *iov_bidi_cnt)
+{
+	int space, iov_cnt = 0, ret = 0;
 
-	if (!cmd || !cmd->dbi_cnt)
-		return true;
+	if (!cmd->dbi_cnt)
+		goto wr_iov_cnts;
 
 	/* try to check and get the data blocks as needed */
 	space = spc_bitmap_free(udev->data_bitmap, udev->dbi_thresh);
@@ -857,10 +874,10 @@ static bool is_ring_space_avail(struct tcmu_dev *udev, struct tcmu_cmd *cmd,
 				(udev->max_blocks - udev->dbi_thresh) + space;
 
 		if (blocks_left < cmd->dbi_cnt) {
-			pr_debug("no data space: only %lu available, but ask for %zu\n",
+			pr_debug("no data space: only %lu available, but ask for %lu\n",
 					blocks_left * DATA_BLOCK_SIZE,
 					cmd->dbi_cnt * DATA_BLOCK_SIZE);
-			return false;
+			return -1;
 		}
 
 		udev->dbi_thresh += cmd->dbi_cnt;
@@ -868,7 +885,19 @@ static bool is_ring_space_avail(struct tcmu_dev *udev, struct tcmu_cmd *cmd,
 			udev->dbi_thresh = udev->max_blocks;
 	}
 
-	return tcmu_get_empty_blocks(udev, cmd);
+	iov_cnt = tcmu_get_empty_blocks(udev, cmd,
+					cmd->dbi_cnt - cmd->dbi_bidi_cnt);
+	if (iov_cnt < 0)
+		return -1;
+
+	if (cmd->dbi_bidi_cnt) {
+		ret = tcmu_get_empty_blocks(udev, cmd, cmd->dbi_bidi_cnt);
+		if (ret < 0)
+			return -1;
+	}
+wr_iov_cnts:
+	*iov_bidi_cnt = ret;
+	return iov_cnt + ret;
 }
 
 static inline size_t tcmu_cmd_get_base_cmd_size(size_t iov_cnt)
@@ -978,7 +1007,7 @@ static int queue_cmd_ring(struct tcmu_cmd *tcmu_cmd, sense_reason_t *scsi_err)
 	struct tcmu_mailbox *mb = udev->mb_addr;
 	struct tcmu_cmd_entry *entry;
 	struct iovec *iov;
-	int iov_cnt, cmd_id;
+	int iov_cnt, iov_bidi_cnt, cmd_id;
 	uint32_t cmd_head;
 	uint64_t cdb_off;
 	bool copy_to_data_area;
@@ -997,42 +1026,54 @@ static int queue_cmd_ring(struct tcmu_cmd *tcmu_cmd, sense_reason_t *scsi_err)
 		return -1;
 	}
 
+	if (!list_empty(&udev->qfull_queue))
+		goto queue;
+
+	if (data_length > udev->data_size) {
+		pr_warn("TCMU: Request of size %zu is too big for %zu data area\n",
+			data_length, udev->data_size);
+		*scsi_err = TCM_INVALID_CDB_FIELD;
+		return -1;
+	}
+
+	iov_cnt = tcmu_alloc_data_space(udev, tcmu_cmd, &iov_bidi_cnt);
+	if (iov_cnt < 0)
+		goto free_and_queue;
+
 	/*
 	 * Must be a certain minimum size for response sense info, but
 	 * also may be larger if the iov array is large.
-	 *
-	 * We prepare as many iovs as possbile for potential uses here,
-	 * because it's expensive to tell how many regions are freed in
-	 * the bitmap & global data pool, as the size calculated here
-	 * will only be used to do the checks.
-	 *
-	 * The size will be recalculated later as actually needed to save
-	 * cmd area memories.
 	 */
-	base_command_size = tcmu_cmd_get_base_cmd_size(tcmu_cmd->dbi_cnt);
+	base_command_size = tcmu_cmd_get_base_cmd_size(iov_cnt);
 	command_size = tcmu_cmd_get_cmd_size(tcmu_cmd, base_command_size);
 
-	if (!list_empty(&udev->qfull_queue))
-		goto queue;
-
-	if ((command_size > (udev->cmdr_size / 2)) ||
-	    data_length > udev->data_size) {
-		pr_warn("TCMU: Request of size %zu/%zu is too big for %u/%zu "
-			"cmd ring/data area\n", command_size, data_length,
-			udev->cmdr_size, udev->data_size);
+	if (command_size > (udev->cmdr_size / 2)) {
+		pr_warn("TCMU: Request of size %zu is too big for %u cmd ring\n",
+			command_size, udev->cmdr_size);
+		tcmu_cmd_free_data(tcmu_cmd, tcmu_cmd->dbi_cur);
 		*scsi_err = TCM_INVALID_CDB_FIELD;
 		return -1;
 	}
 
-	if (!is_ring_space_avail(udev, tcmu_cmd, command_size)) {
+	if (!is_ring_space_avail(udev, command_size))
 		/*
 		 * Don't leave commands partially setup because the unmap
 		 * thread might need the blocks to make forward progress.
 		 */
-		tcmu_cmd_free_data(tcmu_cmd, tcmu_cmd->dbi_cur);
-		tcmu_cmd_reset_dbi_cur(tcmu_cmd);
-		goto queue;
+		goto free_and_queue;
+
+	cmd_id = idr_alloc(&udev->commands, tcmu_cmd, 1, USHRT_MAX, GFP_NOWAIT);
+	if (cmd_id < 0) {
+		pr_err("tcmu: Could not allocate cmd id.\n");
+
+		tcmu_cmd_free_data(tcmu_cmd, tcmu_cmd->dbi_cnt);
+		*scsi_err = TCM_OUT_OF_RESOURCES;
+		return -1;
 	}
+	tcmu_cmd->cmd_id = cmd_id;
+
+	pr_debug("allocated cmd id %u for cmd %p dev %s\n", tcmu_cmd->cmd_id,
+		 tcmu_cmd, udev->name);
 
 	cmd_head = ring_insert_padding(udev, command_size);
 
@@ -1040,52 +1081,27 @@ static int queue_cmd_ring(struct tcmu_cmd *tcmu_cmd, sense_reason_t *scsi_err)
 	memset(entry, 0, command_size);
 	tcmu_hdr_set_op(&entry->hdr.len_op, TCMU_OP_CMD);
 
-	/* Handle allocating space from the data area */
+	/* prepare iov list and copy data to data area if necessary */
 	tcmu_cmd_reset_dbi_cur(tcmu_cmd);
 	iov = &entry->req.iov[0];
-	iov_cnt = 0;
 	copy_to_data_area = (se_cmd->data_direction == DMA_TO_DEVICE
 		|| se_cmd->se_cmd_flags & SCF_BIDI);
 	scatter_data_area(udev, tcmu_cmd, se_cmd->t_data_sg,
-			  se_cmd->t_data_nents, &iov, &iov_cnt,
-			  copy_to_data_area);
-	entry->req.iov_cnt = iov_cnt;
+			  se_cmd->t_data_nents, &iov, copy_to_data_area);
+	entry->req.iov_cnt = iov_cnt - iov_bidi_cnt;
 
 	/* Handle BIDI commands */
-	iov_cnt = 0;
 	if (se_cmd->se_cmd_flags & SCF_BIDI) {
 		iov++;
 		scatter_data_area(udev, tcmu_cmd, se_cmd->t_bidi_data_sg,
-				  se_cmd->t_bidi_data_nents, &iov, &iov_cnt,
-				  false);
+				  se_cmd->t_bidi_data_nents, &iov, false);
+		entry->req.iov_bidi_cnt = iov_bidi_cnt;
 	}
-	entry->req.iov_bidi_cnt = iov_cnt;
-
-	cmd_id = idr_alloc(&udev->commands, tcmu_cmd, 1, USHRT_MAX, GFP_NOWAIT);
-	if (cmd_id < 0) {
-		pr_err("tcmu: Could not allocate cmd id.\n");
-
-		tcmu_cmd_free_data(tcmu_cmd, tcmu_cmd->dbi_cnt);
-		*scsi_err = TCM_OUT_OF_RESOURCES;
-		return -1;
-	}
-	tcmu_cmd->cmd_id = cmd_id;
-
-	pr_debug("allocated cmd id %u for cmd %p dev %s\n", tcmu_cmd->cmd_id,
-		 tcmu_cmd, udev->name);
 
 	tcmu_setup_cmd_timer(tcmu_cmd, udev->cmd_time_out, &udev->cmd_timer);
 
 	entry->hdr.cmd_id = tcmu_cmd->cmd_id;
 
-	/*
-	 * Recalaulate the command's base size and size according
-	 * to the actual needs
-	 */
-	base_command_size = tcmu_cmd_get_base_cmd_size(entry->req.iov_cnt +
-						       entry->req.iov_bidi_cnt);
-	command_size = tcmu_cmd_get_cmd_size(tcmu_cmd, base_command_size);
-
 	tcmu_hdr_set_len(&entry->hdr.len_op, command_size);
 
 	/* All offsets relative to mb_addr, not start of entry! */
@@ -1104,6 +1120,10 @@ static int queue_cmd_ring(struct tcmu_cmd *tcmu_cmd, sense_reason_t *scsi_err)
 
 	return 0;
 
+free_and_queue:
+	tcmu_cmd_free_data(tcmu_cmd, tcmu_cmd->dbi_cur);
+	tcmu_cmd_reset_dbi_cur(tcmu_cmd);
+
 queue:
 	if (add_to_qfull_queue(tcmu_cmd)) {
 		*scsi_err = TCM_OUT_OF_RESOURCES;
@@ -1138,7 +1158,7 @@ queue_tmr_ring(struct tcmu_dev *udev, struct tcmu_tmr *tmr)
 	cmd_size = round_up(sizeof(*entry) + id_list_sz, TCMU_OP_ALIGN_SIZE);
 
 	if (!list_empty(&udev->tmr_queue) ||
-	    !is_ring_space_avail(udev, NULL, cmd_size)) {
+	    !is_ring_space_avail(udev, cmd_size)) {
 		list_add_tail(&tmr->queue_entry, &udev->tmr_queue);
 		pr_debug("adding tmr %p on dev %s to TMR ring space wait queue\n",
 			 tmr, udev->name);