On 2011-04-19 11:09, Jens Axboe wrote:
> On 2011-04-18 20:32, Bart Van Assche wrote:
>> On Mon, Apr 18, 2011 at 8:28 PM, Jens Axboe <jaxboe@xxxxxxxxxxxx> wrote:
>>> On 2011-04-18 20:21, Bart Van Assche wrote:
>>>> a performance regression in the block layer not related to the md
>>>> issue. If I run a small block IOPS test on a block device created by
>>>> ib_srp (NOOP scheduler) I see about 11% less IOPS than with 2.6.38.3
>>>> (155.000 IOPS with 2.6.38.3 and 140.000 IOPS with 2.6.39-rc3+).
>>>
>>> That's not good. What's the test case?
>>
>> Nothing more than a fio IOPS test:
>>
>> fio --bs=512 --ioengine=libaio --buffered=0 --rw=read --thread
>> --iodepth=64 --numjobs=2 --loops=10000 --group_reporting --size=1G
>> --gtod_reduce=1 --name=iops-test --filename=/dev/${dev} --invalidate=1
>
> Bart, can you try the below:
Here's a more complete variant. James, lets get rid of this REENTER
crap. It's completely bogus and triggers falsely for a variety of
reasons. The below will work, but there may be room for improvement on
the SCSI side.
diff --git a/block/blk-core.c b/block/blk-core.c
index 5fa3dd2..4e49665 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -303,15 +303,7 @@ void __blk_run_queue(struct request_queue *q)
if (unlikely(blk_queue_stopped(q)))
return;
- /*
- * Only recurse once to avoid overrunning the stack, let the unplug
- * handling reinvoke the handler shortly if we already got there.
- */
- if (!queue_flag_test_and_set(QUEUE_FLAG_REENTER, q)) {
- q->request_fn(q);
- queue_flag_clear(QUEUE_FLAG_REENTER, q);
- } else
- queue_delayed_work(kblockd_workqueue, &q->delay_work, 0);
+ q->request_fn(q);
}
EXPORT_SYMBOL(__blk_run_queue);
@@ -328,6 +320,7 @@ void blk_run_queue_async(struct request_queue *q)
if (likely(!blk_queue_stopped(q)))
queue_delayed_work(kblockd_workqueue, &q->delay_work, 0);
}
+EXPORT_SYMBOL(blk_run_queue_async);
/**
* blk_run_queue - run a single device queue
diff --git a/block/blk.h b/block/blk.h
index c9df8fc..6126346 100644
--- a/block/blk.h
+++ b/block/blk.h
@@ -22,7 +22,6 @@ void blk_rq_timed_out_timer(unsigned long data);
void blk_delete_timer(struct request *);
void blk_add_timer(struct request *);
void __generic_unplug_device(struct request_queue *);
-void blk_run_queue_async(struct request_queue *q);
/*
* Internal atomic flags for request handling
diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index ab55c2f..e9901b8 100644
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -411,8 +411,6 @@ static void scsi_run_queue(struct request_queue *q)
list_splice_init(&shost->starved_list, &starved_list);
while (!list_empty(&starved_list)) {
- int flagset;
-
/*
* As long as shost is accepting commands and we have
* starved queues, call blk_run_queue. scsi_request_fn
@@ -435,20 +433,7 @@ static void scsi_run_queue(struct request_queue *q)
continue;
}
- spin_unlock(shost->host_lock);
-
- spin_lock(sdev->request_queue->queue_lock);
- flagset = test_bit(QUEUE_FLAG_REENTER, &q->queue_flags) &&
- !test_bit(QUEUE_FLAG_REENTER,
- &sdev->request_queue->queue_flags);
- if (flagset)
- queue_flag_set(QUEUE_FLAG_REENTER, sdev->request_queue);
- __blk_run_queue(sdev->request_queue);
- if (flagset)
- queue_flag_clear(QUEUE_FLAG_REENTER, sdev->request_queue);
- spin_unlock(sdev->request_queue->queue_lock);
-
- spin_lock(shost->host_lock);
+ blk_run_queue_async(sdev->request_queue);
}
/* put any unprocessed entries back */
list_splice(&starved_list, &shost->starved_list);
diff --git a/drivers/scsi/scsi_transport_fc.c b/drivers/scsi/scsi_transport_fc.c
index 28c3350..815069d 100644
--- a/drivers/scsi/scsi_transport_fc.c
+++ b/drivers/scsi/scsi_transport_fc.c
@@ -3816,28 +3816,17 @@ fail_host_msg:
static void
fc_bsg_goose_queue(struct fc_rport *rport)
{
- int flagset;
- unsigned long flags;
-
if (!rport->rqst_q)
return;
+ /*
+ * This get/put dance makes no sense
+ */
get_device(&rport->dev);
-
- spin_lock_irqsave(rport->rqst_q->queue_lock, flags);
- flagset = test_bit(QUEUE_FLAG_REENTER, &rport->rqst_q->queue_flags) &&
- !test_bit(QUEUE_FLAG_REENTER, &rport->rqst_q->queue_flags);
- if (flagset)
- queue_flag_set(QUEUE_FLAG_REENTER, rport->rqst_q);
- __blk_run_queue(rport->rqst_q);
- if (flagset)
- queue_flag_clear(QUEUE_FLAG_REENTER, rport->rqst_q);
- spin_unlock_irqrestore(rport->rqst_q->queue_lock, flags);
-
+ blk_run_queue_async(rport->rqst_q);
put_device(&rport->dev);
}
-
/**
* fc_bsg_rport_dispatch - process rport bsg requests and dispatch to LLDD
* @q: rport request queue
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index cbbfd98..2ad95fa 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -388,20 +388,19 @@ struct request_queue
#define QUEUE_FLAG_SYNCFULL 3 /* read queue has been filled */
#define QUEUE_FLAG_ASYNCFULL 4 /* write queue has been filled */
#define QUEUE_FLAG_DEAD 5 /* queue being torn down */
-#define QUEUE_FLAG_REENTER 6 /* Re-entrancy avoidance */
-#define QUEUE_FLAG_ELVSWITCH 7 /* don't use elevator, just do FIFO */
-#define QUEUE_FLAG_BIDI 8 /* queue supports bidi requests */
-#define QUEUE_FLAG_NOMERGES 9 /* disable merge attempts */
-#define QUEUE_FLAG_SAME_COMP 10 /* force complete on same CPU */
-#define QUEUE_FLAG_FAIL_IO 11 /* fake timeout */
-#define QUEUE_FLAG_STACKABLE 12 /* supports request stacking */
-#define QUEUE_FLAG_NONROT 13 /* non-rotational device (SSD) */
+#define QUEUE_FLAG_ELVSWITCH 6 /* don't use elevator, just do FIFO */
+#define QUEUE_FLAG_BIDI 7 /* queue supports bidi requests */
+#define QUEUE_FLAG_NOMERGES 8 /* disable merge attempts */
+#define QUEUE_FLAG_SAME_COMP 9 /* force complete on same CPU */
+#define QUEUE_FLAG_FAIL_IO 10 /* fake timeout */
+#define QUEUE_FLAG_STACKABLE 11 /* supports request stacking */
+#define QUEUE_FLAG_NONROT 12 /* non-rotational device (SSD) */
#define QUEUE_FLAG_VIRT QUEUE_FLAG_NONROT /* paravirt device */
-#define QUEUE_FLAG_IO_STAT 15 /* do IO stats */
-#define QUEUE_FLAG_DISCARD 16 /* supports DISCARD */
-#define QUEUE_FLAG_NOXMERGES 17 /* No extended merges */
-#define QUEUE_FLAG_ADD_RANDOM 18 /* Contributes to random pool */
-#define QUEUE_FLAG_SECDISCARD 19 /* supports SECDISCARD */
+#define QUEUE_FLAG_IO_STAT 13 /* do IO stats */
+#define QUEUE_FLAG_DISCARD 14 /* supports DISCARD */
+#define QUEUE_FLAG_NOXMERGES 15 /* No extended merges */
+#define QUEUE_FLAG_ADD_RANDOM 16 /* Contributes to random pool */
+#define QUEUE_FLAG_SECDISCARD 17 /* supports SECDISCARD */
#define QUEUE_FLAG_DEFAULT ((1 << QUEUE_FLAG_IO_STAT) | \
(1 << QUEUE_FLAG_STACKABLE) | \
@@ -699,6 +698,7 @@ extern void blk_sync_queue(struct request_queue *q);
extern void __blk_stop_queue(struct request_queue *q);
extern void __blk_run_queue(struct request_queue *q);
extern void blk_run_queue(struct request_queue *);
+extern void blk_run_queue_async(struct request_queue *q);
extern int blk_rq_map_user(struct request_queue *, struct request *,
struct rq_map_data *, void __user *, unsigned long,
gfp_t);
--
Jens Axboe
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