[PATCH] mtip32xx: minor performance enhancements

Sam Bradshaw
2014-06-06T18:50:25Z

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>
---
diff --git a/drivers/block/mtip32xx/mtip32xx.c b/drivers/block/mtip32xx/mtip32xx.c
index 74abd49..fcbac54 100644
--- a/drivers/block/mtip32xx/mtip32xx.c
+++ b/drivers/block/mtip32xx/mtip32xx.c
@@ -2380,6 +2380,8 @@ 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 +2394,7 @@ 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 +2414,7 @@ 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 +2435,7 @@ 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 +3756,7 @@ 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 +3778,11 @@ 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 4b9b554..ba1b31e 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