Re: MMC performance

[Pierre Ossman]

Alan Cox wrote:

> Only on retries. You can try and blast the lot out the first time then
> on retries you write sector by sector.
>
>  
Something like this? Gives more than double throughput here.

Index: linux-wbsd/drivers/mmc/mmc_block.c
===================================================================
--- linux-wbsd/drivers/mmc/mmc_block.c	(revision 71)
+++ linux-wbsd/drivers/mmc/mmc_block.c	(working copy)
@@ -166,9 +166,20 @@
 	struct mmc_blk_data *md = mq->data;
 	struct mmc_card *card = md->queue.card;
 	int ret;
+	int failsafe;
 
 	if (mmc_card_claim_host(card))
 		goto cmd_err;
+	
+	/*
+	 * We first try transfering multiple blocks. If this fails
+	 * we fall back to single block transfers.
+	 *
+	 * This gives us good performance when all is well and the
+	 * possibility to determine which sector fails when all
+	 * is not well.
+	 */
+	failsafe = 0;
 
 	do {
 		struct mmc_blk_request brq;
@@ -188,15 +199,24 @@
 		brq.stop.opcode = MMC_STOP_TRANSMISSION;
 		brq.stop.arg = 0;
 		brq.stop.flags = MMC_RSP_R1B;
+		
+		/*
+		 * A multi-block transfer failed. Falling back to single
+		 * blocks.
+		 */
+		if (failsafe)
+			brq.data.blocks = 1;
+		
+		ret = 1;
 
 		if (rq_data_dir(req) == READ) {
 			brq.cmd.opcode = brq.data.blocks > 1 ? MMC_READ_MULTIPLE_BLOCK : MMC_READ_SINGLE_BLOCK;
 			brq.data.flags |= MMC_DATA_READ;
 		} else {
-			brq.cmd.opcode = MMC_WRITE_BLOCK;
+			brq.cmd.opcode = brq.data.blocks > 1 ? MMC_WRITE_MULTIPLE_BLOCK :
+				MMC_WRITE_BLOCK;
 			brq.cmd.flags = MMC_RSP_R1B;
 			brq.data.flags |= MMC_DATA_WRITE;
-			brq.data.blocks = 1;
 		}
 		brq.mrq.stop = brq.data.blocks > 1 ? &brq.stop : NULL;
 
@@ -204,19 +224,34 @@
 		if (brq.cmd.error) {
 			printk(KERN_ERR "%s: error %d sending read/write command\n",
 			       req->rq_disk->disk_name, brq.cmd.error);
-			goto cmd_err;
+			if (failsafe)
+				goto cmd_err;
+			else {
+				failsafe = 1;
+				continue;
+			}
 		}
 
 		if (brq.data.error) {
 			printk(KERN_ERR "%s: error %d transferring data\n",
 			       req->rq_disk->disk_name, brq.data.error);
-			goto cmd_err;
+			if (failsafe)
+				goto cmd_err;
+			else {
+				failsafe = 1;
+				continue;
+			}
 		}
 
 		if (brq.stop.error) {
 			printk(KERN_ERR "%s: error %d sending stop command\n",
 			       req->rq_disk->disk_name, brq.stop.error);
-			goto cmd_err;
+			if (failsafe)
+				goto cmd_err;
+			else {
+				failsafe = 1;
+				continue;
+			}
 		}
 
 		do {
@@ -229,7 +264,12 @@
 			if (err) {
 				printk(KERN_ERR "%s: error %d requesting status\n",
 				       req->rq_disk->disk_name, err);
-				goto cmd_err;
+				if (failsafe)
+					goto cmd_err;
+				else {
+					failsafe = 1;
+					continue;
+				}
 			}
 		} while (!(cmd.resp[0] & R1_READY_FOR_DATA));
 
@@ -255,6 +295,11 @@
 			end_that_request_last(req);
 		}
 		spin_unlock_irq(&md->lock);
+		
+		/*
+		 * Go back to bulk mode if in failsafe mode.
+		 */
+		failsafe = 0;
 	} while (ret);
 
 	mmc_card_release_host(card);