svn commit: r322863 - head/sys/cam

[Rodney W. Grimes]

[ Charset UTF-8 unsupported, converting... ]
> On Fri, Aug 25, 2017 at 7:35 AM, Slawa Olhovchenkov <slw at zxy.spb.ru> wrote:
> 
> > On Thu, Aug 24, 2017 at 10:11:10PM +0000, Warner Losh wrote:
> >
> > > Author: imp
> > > Date: Thu Aug 24 22:11:10 2017
> > > New Revision: 322863
> > > URL: https://svnweb.freebsd.org/changeset/base/322863
> > >
> > > Log:
> > >   Expand the latency tracking array from 1.024s to 8.192s to help track
> > >   extreme outliers from dodgy drives. Adjust comments to reflect this,
> > >   and make sure that the number of latency buckets match in the two
> > >   places where it matters.
> >
> > May be up to 1min?
> >
> 
> I'm not sure what additional data you'll get between "totally sucks, at
> least 8s latency" and "totally sucks, at least 32s." or "totally sucks, at
> least 64s" though the latter isn't possible with the default timeouts...
> 
> I'm planning on adding a 'max' latency that's self-resetting instead of
> expanding the bucket upwards. I'm also contemplating expanding it down to
> 100us or even 10us since nda serves nvme drives which easily can be sub
> 100us.
> 
> Warner

What about using a log2/log10 engineering style binning of
1, 2, 4, 8 us
10, 20, 40, 80 us
100, 200, 400, 800 us
...
10000000, 20000000, 40000000, 80000000 us

This would give you a fairly fine grain in the high speed
area and cource grain in the not very likely areas, and
it all fits in a nice 32 ints.


-- 
Rod Grimes                                                 rgrimes at freebsd.org