Re: bcache strange behaviour in write back mode

[Jack Wang <jinpu.wang-EIkl63zCoXaH+58JC4qpiA@public.gmane.org>]

On 2013年04月22日 22:19, Kent Overstreet wrote:
> So you can easily reproduce this? If so, that's _awesome_ news - would
> you be willing to try out a debug kernel with some tracing stuff added?
> Maybe we can finally nail this.
> 
> 
Thanks for reply, Kent, two of my colleagues saw this behaviour, so I
think we can reproduce this.
If you could give me more detailed guide to narrow it down, I can try it
on my side.

Regards,
Jack
> On Mon, Apr 22, 2013 at 12:15 PM, Jack Wang <jinpu.wang@profitbricks.com
> <mailto:jinpu.wang-EIkl63zCoXaH+58JC4qpiA@public.gmane.org>> wrote:
> 
>     Hi all,
> 
>     We've seen strange behaviour in bcache mode in current bcache-testing
>     branch with Possible allocator fix:
> 
>     Once I start writing data with "dd if=/dev/zero of=/dev/bcache0 bs=4k
>     count=10000 oflag=sync", all SSDs in the Pool go close to 100% util and
>     I see about 3600 writes/second in iostat for each disk in the pool, BUT
>     no data written in means of throughput.
> 
>     Then after some seconds (the flush interval of bcache) I see the flush
>     of the writeback and also data written to the pool SSDs which looks
>     pretty much like reordering and merging happened for that data.
> 
>     bcache-3.2 does not have such problem.
>     only bcache(master) and bcache-testing have such problem.
> 
>     What's the possible reason?
> 
>     Regards,
>     Jack
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