mtip32xx: minor performance enhancements

This patch adds the following:

1) Compiler hinting in the fast path.
2) A prefetch of port->flags to eliminate moderate cpu stalling later
in mtip_hw_submit_io().
3) Eliminate a redundant rq_data_dir().
4) Reorder members of driver_data to eliminate false cacheline sharing
between irq_workers_active and unal_qdepth.

With some workload and topology configurations, I'm seeing ~1.5%
throughput improvement in small block random read benchmarks as well
as improved latency std. dev.

Signed-off-by: Sam Bradshaw <sbradshaw@micron.com>

Add include of <linux/prefetch.h>

Signed-off-by: Jens Axboe <axboe@fb.com>

2 files changed, 13 insertions, 10 deletions

diff --git a/drivers/block/mtip32xx/mtip32xx.c b/drivers/block/mtip32xx/mtip32xx.c
index 74abd49fabdc..295f3afbbef5 100644
--- a/drivers/block/mtip32xx/mtip32xx.c
+++ b/drivers/block/mtip32xx/mtip32xx.c
@@ -39,6 +39,7 @@
 #include <../drivers/ata/ahci.h>
 #include <linux/export.h>
 #include <linux/debugfs.h>
+#include <linux/prefetch.h>
 #include "mtip32xx.h"
 
 #define HW_CMD_SLOT_SZ          (MTIP_MAX_COMMAND_SLOTS * 32)
@@ -2380,6 +2381,8 @@ static void mtip_hw_submit_io(struct driver_data *dd, struct request *rq,
         /* Map the scatter list for DMA access */
         nents = dma_map_sg(&dd->pdev->dev, command->sg, nents, dma_dir);
 
+        prefetch(&port->flags);
+
         command->scatter_ents = nents;
 
         /*
@@ -2392,7 +2395,7 @@ static void mtip_hw_submit_io(struct driver_data *dd, struct request *rq,
         fis = command->command;
         fis->type        = 0x27;
         fis->opts        = 1 << 7;
-        if (rq_data_dir(rq) == READ)
+        if (dma_dir == DMA_FROM_DEVICE)
                 fis->command = ATA_CMD_FPDMA_READ;
         else
                 fis->command = ATA_CMD_FPDMA_WRITE;
@@ -2412,7 +2415,7 @@ static void mtip_hw_submit_io(struct driver_data *dd, struct request *rq,
         fis->res3        = 0;
         fill_command_sg(dd, command, nents);
 
-        if (command->unaligned)
+        if (unlikely(command->unaligned))
                 fis->device |= 1 << 7;
 
         /* Populate the command header */
@@ -2433,7 +2436,7 @@ static void mtip_hw_submit_io(struct driver_data *dd, struct request *rq,
          * To prevent this command from being issued
          * if an internal command is in progress or error handling is active.
          */
-        if (port->flags & MTIP_PF_PAUSE_IO) {
+        if (unlikely(port->flags & MTIP_PF_PAUSE_IO)) {
                 set_bit(rq->tag, port->cmds_to_issue);
                 set_bit(MTIP_PF_ISSUE_CMDS_BIT, &port->flags);
                 return;
@@ -3754,7 +3757,7 @@ static bool mtip_check_unal_depth(struct blk_mq_hw_ctx *hctx,
         struct driver_data *dd = hctx->queue->queuedata;
         struct mtip_cmd *cmd = blk_mq_rq_to_pdu(rq);
 
-        if (!dd->unal_qdepth || rq_data_dir(rq) == READ)
+        if (rq_data_dir(rq) == READ || !dd->unal_qdepth)
                 return false;
 
         /*
@@ -3776,11 +3779,11 @@ static int mtip_queue_rq(struct blk_mq_hw_ctx *hctx, struct request *rq)
 {
         int ret;
 
-        if (mtip_check_unal_depth(hctx, rq))
+        if (unlikely(mtip_check_unal_depth(hctx, rq)))
                 return BLK_MQ_RQ_QUEUE_BUSY;
 
         ret = mtip_submit_request(hctx, rq);
-        if (!ret)
+        if (likely(!ret))
                 return BLK_MQ_RQ_QUEUE_OK;
 
         rq->errors = ret;
diff --git a/drivers/block/mtip32xx/mtip32xx.h b/drivers/block/mtip32xx/mtip32xx.h
index 4b9b554234bc..ba1b31ee22ec 100644
--- a/drivers/block/mtip32xx/mtip32xx.h
+++ b/drivers/block/mtip32xx/mtip32xx.h
@@ -493,19 +493,19 @@ struct driver_data {
 
         struct workqueue_struct *isr_workq;
 
-        struct mtip_work work[MTIP_MAX_SLOT_GROUPS];
-
         atomic_t irq_workers_active;
 
+        struct mtip_work work[MTIP_MAX_SLOT_GROUPS];
+
         int isr_binding;
 
         struct block_device *bdev;
 
-        int unal_qdepth; /* qdepth of unaligned IO queue */
-
         struct list_head online_list; /* linkage for online list */
 
         struct list_head remove_list; /* linkage for removing list */
+
+        int unal_qdepth; /* qdepth of unaligned IO queue */
 };
 
 #endif