linux-kernel - [PATCH] blkcg: Before starting a new slice, firstly count bps/iops limit in func tg_may

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Date:	Fri, 11 Jan 2013 17:11:28 +0800
From:	majianpeng <majianpeng@...il.com>
To:	axboe <axboe@...nel.dk>
Cc:	linux-kernel <linux-kernel@...r.kernel.org>
Subject: [PATCH] blkcg: Before starting a new slice, firstly count bps/iops limit in func tg_may_dispatch.

In func tg_may_dispatch,
>if (throtl_slice_used(td, tg, rw))
>		throtl_start_new_slice(td, tg, rw);
...
>if (tg_with_in_bps_limit(td, tg, bio, &bps_wait)
>	    && tg_with_in_iops_limit(td, tg, bio, &iops_wait)) {

In funcs tg_with_in_(bps/iops)_limit, it used the slice_start to count.
So if privious slice expired, it start a new slice.This can cause hung
task.

The next steps can repeat this bug.
1:echo "8:48 10240" > blkio.throttle.write_bps_devic
2:dd if=/dev/zero of=/dev/sdd bs=1M count=1 oflag=direct

Using the blktrace, the messages about throttle:
root@...nel:/mnt/programs# blktrace -d /dev/sdd -a notify -o -|blkparse -i -
  8,48   1        0     0.000000000     0  m   N throtl / [W] new slice start=4294854679 end=4294854779 jiffies=4294854679
  8,48   1        0     0.000000966     0  m   N throtl / [W] extend slice start=4294854679 end=4294905900 jiffies=4294854679
  8,48   1        0     0.000002553     0  m   N throtl / [W] bio. bdisp=0 sz=524288 bps=10240 iodisp=0 iops=4294967295 queued=0/0
  8,48   1        0     0.000004788     0  m   N throtl schedule work. delay=51200 jiffies=4294854679
  8,48   1        0    51.304698681     0  m   N throtl dispatch nr_queued=1 read=0 write=1
  8,48   1        0    51.304701979     0  m   N throtl / [W] new slice start=4294905984 end=4294906084 jiffies=4294905984
  8,48   1        0    51.304703329     0  m   N throtl / [W] extend slice start=4294905984 end=4294957200 jiffies=4294905984
  8,48   1        0    51.304705783     0  m   N throtl schedule work. delay=51200 jiffies=4294905984
  8,48   1        0   102.632697082     0  m   N throtl dispatch nr_queued=1 read=0 write=1
  8,48   1        0   102.632700544     0  m   N throtl / [W] new slice start=4294957312 end=4294957412 jiffies=4294957312
  8,48   1        0   102.632701922     0  m   N throtl / [W] extend slice start=4294957312 end=4295008600 jiffies=4294957312
  8,48   1        0   102.632704016     0  m   N throtl schedule work. delay=51200 jiffies=4294957312
  8,48   1        0   153.960696503     0  m   N throtl dispatch nr_queued=1 read=0 write=1
  8,48   1        0   153.960699797     0  m   N throtl / [W] new slice start=4295008640 end=4295008740 jiffies=4295008640
  8,48   1        0   153.960701153     0  m   N throtl / [W] extend slice start=4295008640 end=4295059900 jiffies=4295008640
  8,48   1        0   153.960703218     0  m   N throtl schedule work. delay=51200 jiffies=4295008640
  8,48   1        0   205.288697067     0  m   N throtl dispatch nr_queued=1 read=0 write=1
  8,48   1        0   205.288700268     0  m   N throtl / [W] new slice start=4295059968 end=4295060068 jiffies=4295059968
  8,48   1        0   205.288701630     0  m   N throtl / [W] extend slice start=4295059968 end=4295111200 jiffies=4295059968
  8,48   1        0   205.288703784     0  m   N throtl schedule work. delay=51200 jiffies=4295059968
  8,48   1        0   256.616696184     0  m   N throtl dispatch nr_queued=1 read=0 write=1
  8,48   1        0   256.616699266     0  m   N throtl / [W] new slice start=4295111296 end=4295111396 jiffies=4295111296
  8,48   1        0   256.616700574     0  m   N throtl / [W] extend slice start=4295111296 end=4295162500 jiffies=4295111296
  8,48   1        0   256.616702701     0  m   N throtl schedule work. delay=51200 jiffies=4295111296

Signed-off-by: Jianpeng Ma <majianpeng@...il.com>
---
 block/blk-throttle.c |   15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 deletions(-)

diff --git a/block/blk-throttle.c b/block/blk-throttle.c
index 3114622..9258789 100644
--- a/block/blk-throttle.c
+++ b/block/blk-throttle.c
@@ -645,6 +645,15 @@ static bool tg_may_dispatch(struct throtl_data *td, struct throtl_grp *tg,
 	}
 
 	/*
+	 * If privious slice expired,then start new slice.
+	 * But counting bps and iops limit need privious slice info
+	 * which ->slice_start.
+	 */
+	if (tg_with_in_bps_limit(td, tg, bio, &bps_wait)
+	    && tg_with_in_iops_limit(td, tg, bio, &iops_wait))
+		if (wait)
+			*wait = 0;
+	/*
 	 * If previous slice expired, start a new one otherwise renew/extend
 	 * existing slice to make sure it is at least throtl_slice interval
 	 * long since now.
@@ -656,12 +665,8 @@ static bool tg_may_dispatch(struct throtl_data *td, struct throtl_grp *tg,
 			throtl_extend_slice(td, tg, rw, jiffies + throtl_slice);
 	}
 
-	if (tg_with_in_bps_limit(td, tg, bio, &bps_wait)
-	    && tg_with_in_iops_limit(td, tg, bio, &iops_wait)) {
-		if (wait)
-			*wait = 0;
+	if (!(bps_wait || iops_wait))
 		return 1;
-	}
 
 	max_wait = max(bps_wait, iops_wait);
 
-- 
1.7.9.5


Jianpeng Ma
Thanks!