Re: [PATCH] blk-throttle: fix zero wait time for iops throttled group

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



On 08.07.2019 22:08, Liu Bo wrote:
On Mon, Jul 08, 2019 at 06:29:57PM +0300, Konstantin Khlebnikov wrote:
After commit 991f61fe7e1d ("Blk-throttle: reduce tail io latency when iops
limit is enforced") wait time could be zero even if group is throttled and
cannot issue requests right now. As a result throtl_select_dispatch() turns
into busy-loop under irq-safe queue spinlock.

Fix is simple: always round up target time to the next throttle slice.

Fixes: 991f61fe7e1d ("Blk-throttle: reduce tail io latency when iops limit is enforced")
Signed-off-by: Konstantin Khlebnikov <khlebnikov@xxxxxxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx # v4.19+
---
  block/blk-throttle.c |    9 +++------
  1 file changed, 3 insertions(+), 6 deletions(-)

diff --git a/block/blk-throttle.c b/block/blk-throttle.c
index 9ea7c0ecad10..8ab6c8153223 100644
--- a/block/blk-throttle.c
+++ b/block/blk-throttle.c
@@ -881,13 +881,10 @@ static bool tg_with_in_iops_limit(struct throtl_grp *tg, struct bio *bio,
  	unsigned long jiffy_elapsed, jiffy_wait, jiffy_elapsed_rnd;
  	u64 tmp;
- jiffy_elapsed = jiffy_elapsed_rnd = jiffies - tg->slice_start[rw];
-
-	/* Slice has just started. Consider one slice interval */
-	if (!jiffy_elapsed)
-		jiffy_elapsed_rnd = tg->td->throtl_slice;
+	jiffy_elapsed = jiffies - tg->slice_start[rw];
- jiffy_elapsed_rnd = roundup(jiffy_elapsed_rnd, tg->td->throtl_slice);
+	/* Round up to the next throttle slice, wait time must be nonzero */
+	jiffy_elapsed_rnd = roundup(jiffy_elapsed + 1, tg->td->throtl_slice);
/*
  	 * jiffy_elapsed_rnd should not be a big value as minimum iops can be

Did you use a tiny iops limit to run into this?

Yep. 25 iops

also kernel built with HZ=250, this might be related


thanks,
-liubo




[Index of Archives]     [Linux RAID]     [Linux SCSI]     [Linux ATA RAID]     [IDE]     [Linux Wireless]     [Linux Kernel]     [ATH6KL]     [Linux Bluetooth]     [Linux Netdev]     [Kernel Newbies]     [Security]     [Git]     [Netfilter]     [Bugtraq]     [Yosemite News]     [MIPS Linux]     [ARM Linux]     [Linux Security]     [Device Mapper]

  Powered by Linux