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Subjectio_request_lock/queue_lock patch

Included below is a snapshot of a patch I am developing to reduce
io_request_lock contention in 2.4.

This patch changes __make_request to take the device-specific queue_lock
instead of io_request_lock and changes generic_unplug_device to take
queue_lock in addition to io_request_lock to serialize access to the
request queue. Also, locking in various functions has been modified
in accordance with this new scheme.

I have done some testing of this with aic7xxx, qla2x00, and lpfc adapters.

To apply it to 2.4.6 or 2.4.7, from linux/ "patch -p1 < iorlv0_247".

Comments and suggestions are welcome and invited.

Jonathan

----- patch -----
diff -Naur linux.base/drivers/block/ll_rw_blk.c linux.mod/drivers/block/ll_rw_blk.c
--- linux.base/drivers/block/ll_rw_blk.c Thu Jul 19 20:51:23 2001
+++ linux.mod/drivers/block/ll_rw_blk.c Fri Aug 24 10:17:38 2001
@@ -343,11 +343,13 @@
void generic_unplug_device(void *data)
{
request_queue_t *q = (request_queue_t *) data;
- unsigned long flags;
+ unsigned long flags[2];

- spin_lock_irqsave(&io_request_lock, flags);
+ spin_lock_irqsave(&io_request_lock, flags[0]);
+ spin_lock_irqsave(&q->queue_lock, flags[1]);
__generic_unplug_device(q);
- spin_unlock_irqrestore(&io_request_lock, flags);
+ spin_unlock_irqrestore(&q->queue_lock, flags[1]);
+ spin_unlock_irqrestore(&io_request_lock, flags[0]);
}

static void blk_init_free_list(request_queue_t *q)
@@ -470,9 +472,9 @@
add_wait_queue_exclusive(&q->wait_for_request, &wait);
for (;;) {
__set_current_state(TASK_UNINTERRUPTIBLE);
- spin_lock_irq(&io_request_lock);
+ spin_lock_irq(&q->queue_lock);
rq = get_request(q, rw);
- spin_unlock_irq(&io_request_lock);
+ spin_unlock_irq(&q->queue_lock);
if (rq)
break;
generic_unplug_device(q);
@@ -487,9 +489,9 @@
{
register struct request *rq;

- spin_lock_irq(&io_request_lock);
+ spin_lock_irq(&q->queue_lock);
rq = get_request(q, rw);
- spin_unlock_irq(&io_request_lock);
+ spin_unlock_irq(&q->queue_lock);
if (rq)
return rq;
return __get_request_wait(q, rw);
@@ -555,7 +557,7 @@
drive_stat_acct(req->rq_dev, req->cmd, req->nr_sectors, 1);

if (!q->plugged && q->head_active && insert_here == &q->queue_head) {
- spin_unlock_irq(&io_request_lock);
+ spin_unlock_irq(&q->queue_lock);
BUG();
}

@@ -727,7 +729,7 @@
* Now we acquire the request spinlock, we have to be mega careful
* not to schedule or do something nonatomic
*/
- spin_lock_irq(&io_request_lock);
+ spin_lock_irq(&q->queue_lock);

insert_here = head->prev;
if (list_empty(head)) {
@@ -794,7 +796,7 @@
req = freereq;
freereq = NULL;
} else if ((req = get_request(q, rw)) == NULL) {
- spin_unlock_irq(&io_request_lock);
+ spin_unlock_irq(&q->queue_lock);
if (rw_ahead)
goto end_io;

@@ -821,7 +823,7 @@
out:
if (freereq)
blkdev_release_request(freereq);
- spin_unlock_irq(&io_request_lock);
+ spin_unlock_irq(&q->queue_lock);
return 0;
end_io:
bh->b_end_io(bh, test_bit(BH_Uptodate, &bh->b_state));
diff -Naur linux.base/drivers/scsi/scsi.c linux.mod/drivers/scsi/scsi.c
--- linux.base/drivers/scsi/scsi.c Thu Jul 19 21:07:04 2001
+++ linux.mod/drivers/scsi/scsi.c Fri Aug 24 11:06:25 2001
@@ -678,41 +678,33 @@
* passes a meaningful return value.
*/
if (host->hostt->use_new_eh_code) {
- spin_lock_irqsave(&io_request_lock, flags);
rtn = host->hostt->queuecommand(SCpnt, scsi_done);
- spin_unlock_irqrestore(&io_request_lock, flags);
if (rtn != 0) {
scsi_delete_timer(SCpnt);
scsi_mlqueue_insert(SCpnt, SCSI_MLQUEUE_HOST_BUSY);
SCSI_LOG_MLQUEUE(3, printk("queuecommand : request rejected\n"));
}
} else {
- spin_lock_irqsave(&io_request_lock, flags);
host->hostt->queuecommand(SCpnt, scsi_old_done);
- spin_unlock_irqrestore(&io_request_lock, flags);
}
} else {
int temp;

SCSI_LOG_MLQUEUE(3, printk("command() : routine at %p\n", host->hostt->command));
- spin_lock_irqsave(&io_request_lock, flags);
temp = host->hostt->command(SCpnt);
SCpnt->result = temp;
#ifdef DEBUG_DELAY
- spin_unlock_irqrestore(&io_request_lock, flags);
clock = jiffies + 4 * HZ;
while (time_before(jiffies, clock))
barrier();
printk("done(host = %d, result = %04x) : routine at %p\n",
host->host_no, temp, host->hostt->command);
- spin_lock_irqsave(&io_request_lock, flags);
#endif
if (host->hostt->use_new_eh_code) {
scsi_done(SCpnt);
} else {
scsi_old_done(SCpnt);
}
- spin_unlock_irqrestore(&io_request_lock, flags);
}
SCSI_LOG_MLQUEUE(3, printk("leaving scsi_dispatch_cmnd()\n"));
return rtn;
diff -Naur linux.base/drivers/scsi/scsi_lib.c linux.mod/drivers/scsi/scsi_lib.c
--- linux.base/drivers/scsi/scsi_lib.c Thu Jul 19 20:48:04 2001
+++ linux.mod/drivers/scsi/scsi_lib.c Fri Aug 24 10:19:50 2001
@@ -68,7 +68,7 @@
static void __scsi_insert_special(request_queue_t *q, struct request *rq,
void *data, int at_head)
{
- unsigned long flags;
+ unsigned long flags[2];

ASSERT_LOCK(&io_request_lock, 0);

@@ -84,7 +84,8 @@
* head of the queue for things like a QUEUE_FULL message from a
* device, or a host that is unable to accept a particular command.
*/
- spin_lock_irqsave(&io_request_lock, flags);
+ spin_lock_irqsave(&io_request_lock, flags[0]);
+ spin_lock_irqsave(&q->queue_lock, flags[1]);

if (at_head)
list_add(&rq->queue, &q->queue_head);
@@ -92,7 +93,8 @@
list_add_tail(&rq->queue, &q->queue_head);

q->request_fn(q);
- spin_unlock_irqrestore(&io_request_lock, flags);
+ spin_unlock_irqrestore(&q->queue_lock, flags[1]);
+ spin_unlock_irqrestore(&io_request_lock, flags[0]);
}


@@ -246,13 +248,14 @@
void scsi_queue_next_request(request_queue_t * q, Scsi_Cmnd * SCpnt)
{
int all_clear;
- unsigned long flags;
+ unsigned long flags[2];
Scsi_Device *SDpnt;
struct Scsi_Host *SHpnt;

ASSERT_LOCK(&io_request_lock, 0);

- spin_lock_irqsave(&io_request_lock, flags);
+ spin_lock_irqsave(&io_request_lock, flags[0]);
+ spin_lock_irqsave(&q->queue_lock, flags[1]);
if (SCpnt != NULL) {

/*
@@ -328,7 +331,8 @@
SHpnt->some_device_starved = 0;
}
}
- spin_unlock_irqrestore(&io_request_lock, flags);
+ spin_unlock_irqrestore(&q->queue_lock, flags[1]);
+ spin_unlock_irqrestore(&io_request_lock, flags[0]);
}

/*
@@ -821,6 +825,7 @@
struct Scsi_Device_Template *STpnt;

ASSERT_LOCK(&io_request_lock, 1);
+ ASSERT_LOCK(&q->queue_lock, 1);

SDpnt = (Scsi_Device *) q->queuedata;
if (!SDpnt) {
@@ -828,6 +833,7 @@
}
SHpnt = SDpnt->host;

+
/*
* To start with, we keep looping until the queue is empty, or until
* the host is no longer able to accept any more requests.
@@ -839,7 +845,7 @@
* we need to check to see if the queue is plugged or not.
*/
if (SHpnt->in_recovery || q->plugged)
- return;
+ break;

/*
* If the device cannot accept another request, then quit.
@@ -887,9 +893,11 @@
*/
SDpnt->was_reset = 0;
if (SDpnt->removable && !in_interrupt()) {
+ spin_unlock_irq(&q->queue_lock);
spin_unlock_irq(&io_request_lock);
scsi_ioctl(SDpnt, SCSI_IOCTL_DOORLOCK, 0);
spin_lock_irq(&io_request_lock);
+ spin_lock_irq(&q->queue_lock);
continue;
}
}
@@ -998,8 +1006,6 @@
* another.
*/
req = NULL;
- spin_unlock_irq(&io_request_lock);
-
if (SCpnt->request.cmd != SPECIAL) {
/*
* This will do a couple of things:
@@ -1028,7 +1034,6 @@
{
panic("Should not have leftover blocks\n");
}
- spin_lock_irq(&io_request_lock);
SHpnt->host_busy--;
SDpnt->device_busy--;
continue;
@@ -1044,7 +1049,6 @@
{
panic("Should not have leftover blocks\n");
}
- spin_lock_irq(&io_request_lock);
SHpnt->host_busy--;
SDpnt->device_busy--;
continue;
@@ -1065,7 +1069,6 @@
* Now we need to grab the lock again. We are about to mess
* with the request queue and try to find another command.
*/
- spin_lock_irq(&io_request_lock);
}
}

-
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