Re: bcache kernel 3.10 wrong bypassed values

[Kent Overstreet <kmo-PEzghdH756F8UrSeD/g0lQ@public.gmane.org>]

On Fri, Jul 12, 2013 at 08:13:36AM +0200, Stefan Priebe - Profihost AG wrote:
> Am 12.07.2013 03:55, schrieb Kent Overstreet:
> > On Thu, Jul 04, 2013 at 10:13:20AM +0200, Stefan Priebe - Profihost AG wrote:
> >> Hello list,
> >>
> >> while testing bcache i noticed that while writing a big 48GB file the
> >> sequential cutoff works fine i see only I/O on the disk but not on the
> >> cache. I thought i would afterwards see a bypassed value of around 48GB
> >> but it is only 1.2GB.
> >>
> >> Is this expected? Is bcache in kernel 3.10 stable for production usage?
> > 
> > That sounds like a bug, but bcache in 3.10 certainly should be stable
> > for production usage.
> > 
> > There can be some weirdness due to the way the stats work, there's a ~13
> > second update interval (and also the intermediate counters are 32 bit
> > ints so if you manage to wrap that in 13 seconds you'll lose counts, but
> > it's counting sectors so I doubt that happened here).
> 
> Mhm i doubt that too. But if i write 40GB shouldn't i see a bypass value
> near 40GB? It's just very small.
> 
> > Does that sound like it might explain what you were seeing, or do you
> > think there's something else going on?
> No right no i don't believe that.

Have you noticed any pattern to it? Does it appear to sometimes be right
and sometimes wrong, or is it always wrong?

I looked again at the code that updates that value and I'm not coming up
with any ideas to explain what you're seeing...