Re: wrong in_flight diskstat in 2.6.16.1

[Jens Axboe <axboe@suse.de>]

On Tue, May 23 2006, Martin Devera wrote:
> Jens Axboe wrote:
> >On Tue, May 23 2006, Martin Devera wrote:
> >>Hello,
> >>
> >>I see weird output from /sys/block/sd{a,b}/stat on our AMD64-X2 smp 
> >>machine with HT1000 (Broadcom) SATA with 2 WD 250GB HDDs in MD raid1. AS 
> >>scheduler was used, change to noop didn't change anything. It is vanilla 
> >>2.6.16.1 and here are absolute values in hex and one second differences 
> >>below:
> >>
> >>132CDF 56D62 61753C0 6966BC 165A8EB 5FF5B6C 3B32D6C0 1110594C FFCA89A4 
> >>FEE85878 49FF74E4
> >>132CDF 56D62 61753C0 6966BC 165A8EF 5FF5B6C 3B32D6E0 111059D0 FFCA89A1 
> >>FEE85C60 79291244
> >> 0: 0
> >> 1: 0
> >> 2: 0
> >> 3: 0
> >> 4: 4
> >> 5: 0
> >> 6: 32
> >> 7: 132
> >> 8: -3
> >> 9: 1000
> >>10: 791256416
> >>
> >>As you can see in_flight is constantly negative and it is DECREASING 
> >>slowly all the time.
> >>I can't find any reason for it :-\
> >
> >Are you using io barriers?
> >
> >[PATCH] blk: fix gendisk->in_flight accounting during barrier sequence
> 
> I don't think so, I just used
> mount / -o remount,barrier=0
> to make it sure and it keeps decrementing. I'll however apply the patch 
> (and others up to 2.6.16.18) at night (I'm not allowed to restart the 
> machine just now).

Ah, but you are using md, which uses barriers for superblock updates. So
the patch will likely help you.

-- 
Jens Axboe

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