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authorBoaz Harrosh <bharrosh@panasas.com>2009-03-24 12:23:40 +0100
committerJens Axboe <jens.axboe@oracle.com>2009-03-24 12:35:17 +0100
commit05378940caf979a8655c18b18a17213dcfa52412 (patch)
treeb72d29396fd6aa6f4485af638090066c7280325b /block/bsg.c
parent0061d38642244892e17156f005bd7055fe744644 (diff)
downloadlinux-linaro-stable-05378940caf979a8655c18b18a17213dcfa52412.tar.gz
bsg: add support for tail queuing
Currently inherited from sg.c bsg will submit asynchronous request at the head-of-the-queue, (using "at_head" set in the call to blk_execute_rq_nowait()). This is bad in situation where the queues are full, requests will execute out of order, and can cause starvation of the first submitted requests. The sg_io_v4->flags member is used and a bit is allocated to denote the Q_AT_TAIL. Zero is to queue at_head as before, to be compatible with old code at the write/read path. SG_IO code path behavior was changed so to be the same as write/read behavior. SG_IO was very rarely used and breaking compatibility with it is OK at this stage. sg_io_hdr at sg.h also has a flags member and uses 3 bits from the first nibble and one bit from the last nibble. Even though none of these bits are supported by bsg, The second nibble is allocated for use by bsg. Just in case. Signed-off-by: Boaz Harrosh <bharrosh@panasas.com> CC: Douglas Gilbert <dgilbert@interlog.com> Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
Diffstat (limited to 'block/bsg.c')
-rw-r--r--block/bsg.c9
1 files changed, 7 insertions, 2 deletions
diff --git a/block/bsg.c b/block/bsg.c
index 0ce8806dd0c1..0f63b91d0af6 100644
--- a/block/bsg.c
+++ b/block/bsg.c
@@ -353,6 +353,8 @@ static void bsg_rq_end_io(struct request *rq, int uptodate)
static void bsg_add_command(struct bsg_device *bd, struct request_queue *q,
struct bsg_command *bc, struct request *rq)
{
+ int at_head = (0 == (bc->hdr.flags & BSG_FLAG_Q_AT_TAIL));
+
/*
* add bc command to busy queue and submit rq for io
*/
@@ -368,7 +370,7 @@ static void bsg_add_command(struct bsg_device *bd, struct request_queue *q,
dprintk("%s: queueing rq %p, bc %p\n", bd->name, rq, bc);
rq->end_io_data = bc;
- blk_execute_rq_nowait(q, NULL, rq, 1, bsg_rq_end_io);
+ blk_execute_rq_nowait(q, NULL, rq, at_head, bsg_rq_end_io);
}
static struct bsg_command *bsg_next_done_cmd(struct bsg_device *bd)
@@ -924,6 +926,7 @@ static long bsg_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
struct request *rq;
struct bio *bio, *bidi_bio = NULL;
struct sg_io_v4 hdr;
+ int at_head;
u8 sense[SCSI_SENSE_BUFFERSIZE];
if (copy_from_user(&hdr, uarg, sizeof(hdr)))
@@ -936,7 +939,9 @@ static long bsg_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
bio = rq->bio;
if (rq->next_rq)
bidi_bio = rq->next_rq->bio;
- blk_execute_rq(bd->queue, NULL, rq, 0);
+
+ at_head = (0 == (hdr.flags & BSG_FLAG_Q_AT_TAIL));
+ blk_execute_rq(bd->queue, NULL, rq, at_head);
ret = blk_complete_sgv4_hdr_rq(rq, &hdr, bio, bidi_bio);
if (copy_to_user(uarg, &hdr, sizeof(hdr)))