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Commit 98ccf149 authored by Pierre Ossman's avatar Pierre Ossman
Browse files

mmc: bounce requests for simple hosts 



Some hosts cannot do scatter/gather in hardware. Since not doing sg
is such a big performance hit, we (optionally) bounce the requests
to a simple linear buffer that we hand over to the driver.

Signed-off-by: default avatarPierre Ossman <drzeus@drzeus.cx>
parent 7dcca30a

drivers/mmc/card/Kconfig

+18 −0
Original line number Diff line number Diff line
@@ -14,3 +14,21 @@ config MMC_BLOCK 
	  mount the filesystem. Almost everyone wishing MMC support

	  should say Y or M here.



config MMC_BLOCK_BOUNCE

	bool "Use bounce buffer for simple hosts"

	depends on MMC_BLOCK

	default y

	help

	  SD/MMC is a high latency protocol where it is crucial to

	  send large requests in order to get high performance. Many

	  controllers, however, are restricted to continuous memory

	  (i.e. they can't do scatter-gather), something the kernel

	  rarely can provide.



	  Say Y here to help these restricted hosts by bouncing

	  requests back and forth from a large buffer. You will get

	  a big performance gain at the cost of up to 64 KiB of

	  physical memory.



	  If unsure, say Y here.

drivers/mmc/card/block.c

+6 −1
Original line number Diff line number Diff line
@@ -262,7 +262,9 @@ static int mmc_blk_issue_rq(struct mmc_queue *mq, struct request *req) 
		}



		brq.data.sg = mq->sg;

		brq.data.sg_len = blk_rq_map_sg(req->q, req, brq.data.sg);

		brq.data.sg_len = mmc_queue_map_sg(mq);



		mmc_queue_bounce_pre(mq);



		if (brq.data.blocks !=

		    (req->nr_sectors >> (md->block_bits - 9))) {
@@ -279,6 +281,9 @@ static int mmc_blk_issue_rq(struct mmc_queue *mq, struct request *req) 
		}



		mmc_wait_for_req(card->host, &brq.mrq);



		mmc_queue_bounce_post(mq);



		if (brq.cmd.error) {

			printk(KERN_ERR "%s: error %d sending read/write command\n",

			       req->rq_disk->disk_name, brq.cmd.error);

drivers/mmc/card/queue.c

+177 −14
Original line number Diff line number Diff line
@@ -17,6 +17,8 @@ 
#include <linux/mmc/host.h>

#include "queue.h"



#define MMC_QUEUE_BOUNCESZ	65536



#define MMC_QUEUE_SUSPENDED	(1 << 0)



/*
@@ -118,6 +120,7 @@ int mmc_init_queue(struct mmc_queue *mq, struct mmc_card *card, spinlock_t *lock 
	struct mmc_host *host = card->host;

	u64 limit = BLK_BOUNCE_HIGH;

	int ret;

	unsigned int bouncesz;



	if (mmc_dev(host)->dma_mask && *mmc_dev(host)->dma_mask)

		limit = *mmc_dev(host)->dma_mask;
@@ -127,36 +130,83 @@ int mmc_init_queue(struct mmc_queue *mq, struct mmc_card *card, spinlock_t *lock 
	if (!mq->queue)

		return -ENOMEM;



	mq->queue->queuedata = mq;

	mq->req = NULL;



	blk_queue_prep_rq(mq->queue, mmc_prep_request);



#ifdef CONFIG_MMC_BLOCK_BOUNCE

	if (host->max_hw_segs == 1) {

		bouncesz = MMC_QUEUE_BOUNCESZ;



		if (bouncesz > host->max_req_size)

			bouncesz = host->max_req_size;

		if (bouncesz > host->max_seg_size)

			bouncesz = host->max_seg_size;



		mq->bounce_buf = kmalloc(bouncesz, GFP_KERNEL);

		if (!mq->bounce_buf) {

			printk(KERN_WARNING "%s: unable to allocate "

				"bounce buffer\n", mmc_card_name(card));

		} else {

			blk_queue_bounce_limit(mq->queue, BLK_BOUNCE_HIGH);

			blk_queue_max_sectors(mq->queue, bouncesz / 512);

			blk_queue_max_phys_segments(mq->queue, bouncesz / 512);

			blk_queue_max_hw_segments(mq->queue, bouncesz / 512);

			blk_queue_max_segment_size(mq->queue, bouncesz);



			mq->sg = kmalloc(sizeof(struct scatterlist),

				GFP_KERNEL);

			if (!mq->sg) {

				ret = -ENOMEM;

				goto free_bounce_buf;

			}



			mq->bounce_sg = kmalloc(sizeof(struct scatterlist) *

				bouncesz / 512, GFP_KERNEL);

			if (!mq->bounce_sg) {

				ret = -ENOMEM;

				goto free_sg;

			}

		}

	}

#endif



	if (!mq->bounce_buf) {

		blk_queue_bounce_limit(mq->queue, limit);

		blk_queue_max_sectors(mq->queue, host->max_req_size / 512);

		blk_queue_max_phys_segments(mq->queue, host->max_phys_segs);

		blk_queue_max_hw_segments(mq->queue, host->max_hw_segs);

		blk_queue_max_segment_size(mq->queue, host->max_seg_size);



	mq->queue->queuedata = mq;

	mq->req = NULL;



	mq->sg = kmalloc(sizeof(struct scatterlist) * host->max_phys_segs,

			 GFP_KERNEL);

		mq->sg = kmalloc(sizeof(struct scatterlist) *

			host->max_phys_segs, GFP_KERNEL);

		if (!mq->sg) {

			ret = -ENOMEM;

			goto cleanup_queue;

		}

	}



	init_MUTEX(&mq->thread_sem);



	mq->thread = kthread_run(mmc_queue_thread, mq, "mmcqd");

	if (IS_ERR(mq->thread)) {

		ret = PTR_ERR(mq->thread);

		goto free_sg;

		goto free_bounce_sg;

	}



	return 0;



 free_bounce_sg:

 	if (mq->bounce_sg)

 		kfree(mq->bounce_sg);

 	mq->bounce_sg = NULL;

 free_sg:

	kfree(mq->sg);

	mq->sg = NULL;

 free_bounce_buf:

	if (mq->bounce_buf)

		kfree(mq->bounce_buf);

	mq->bounce_buf = NULL;

 cleanup_queue:

	blk_cleanup_queue(mq->queue);

	return ret;
@@ -178,9 +228,17 @@ void mmc_cleanup_queue(struct mmc_queue *mq) 
	/* Then terminate our worker thread */

	kthread_stop(mq->thread);



 	if (mq->bounce_sg)

 		kfree(mq->bounce_sg);

 	mq->bounce_sg = NULL;



	kfree(mq->sg);

	mq->sg = NULL;



	if (mq->bounce_buf)

		kfree(mq->bounce_buf);

	mq->bounce_buf = NULL;



	blk_cleanup_queue(mq->queue);



	mq->card = NULL;
@@ -231,3 +289,108 @@ void mmc_queue_resume(struct mmc_queue *mq) 
	}

}



static void copy_sg(struct scatterlist *dst, unsigned int dst_len,

	struct scatterlist *src, unsigned int src_len)

{

	unsigned int chunk;

	char *dst_buf, *src_buf;

	unsigned int dst_size, src_size;



	dst_buf = NULL;

	src_buf = NULL;

	dst_size = 0;

	src_size = 0;



	while (src_len) {

		BUG_ON(dst_len == 0);



		if (dst_size == 0) {

			dst_buf = page_address(dst->page) + dst->offset;

			dst_size = dst->length;

		}



		if (src_size == 0) {

			src_buf = page_address(src->page) + src->offset;

			src_size = src->length;

		}



		chunk = min(dst_size, src_size);



		memcpy(dst_buf, src_buf, chunk);



		dst_buf += chunk;

		src_buf += chunk;

		dst_size -= chunk;

		src_size -= chunk;



		if (dst_size == 0) {

			dst++;

			dst_len--;

		}



		if (src_size == 0) {

			src++;

			src_len--;

		}

	}

}



unsigned int mmc_queue_map_sg(struct mmc_queue *mq)

{

	unsigned int sg_len;



	if (!mq->bounce_buf)

		return blk_rq_map_sg(mq->queue, mq->req, mq->sg);



	BUG_ON(!mq->bounce_sg);



	sg_len = blk_rq_map_sg(mq->queue, mq->req, mq->bounce_sg);



	mq->bounce_sg_len = sg_len;



	/*

	 * Shortcut in the event we only get a single entry.

	 */

	if (sg_len == 1) {

		memcpy(mq->sg, mq->bounce_sg, sizeof(struct scatterlist));

		return 1;

	}



	mq->sg[0].page = virt_to_page(mq->bounce_buf);

	mq->sg[0].offset = offset_in_page(mq->bounce_buf);

	mq->sg[0].length = 0;



	while (sg_len) {

		mq->sg[0].length += mq->bounce_sg[sg_len - 1].length;

		sg_len--;

	}



	return 1;

}



void mmc_queue_bounce_pre(struct mmc_queue *mq)

{

	if (!mq->bounce_buf)

		return;



	if (mq->bounce_sg_len == 1)

		return;

	if (rq_data_dir(mq->req) != WRITE)

		return;



	copy_sg(mq->sg, 1, mq->bounce_sg, mq->bounce_sg_len);

}



void mmc_queue_bounce_post(struct mmc_queue *mq)

{

	if (!mq->bounce_buf)

		return;



	if (mq->bounce_sg_len == 1)

		return;

	if (rq_data_dir(mq->req) != READ)

		return;



	copy_sg(mq->bounce_sg, mq->bounce_sg_len, mq->sg, 1);

}

drivers/mmc/card/queue.h

+7 −0
Original line number Diff line number Diff line
@@ -14,6 +14,9 @@ struct mmc_queue { 
	void			*data;

	struct request_queue	*queue;

	struct scatterlist	*sg;

	char			*bounce_buf;

	struct scatterlist	*bounce_sg;

	unsigned int		bounce_sg_len;

};



extern int mmc_init_queue(struct mmc_queue *, struct mmc_card *, spinlock_t *);
@@ -21,4 +24,8 @@ extern void mmc_cleanup_queue(struct mmc_queue *); 
extern void mmc_queue_suspend(struct mmc_queue *);

extern void mmc_queue_resume(struct mmc_queue *);



extern unsigned int mmc_queue_map_sg(struct mmc_queue *);

extern void mmc_queue_bounce_pre(struct mmc_queue *);

extern void mmc_queue_bounce_post(struct mmc_queue *);



#endif