Date: Fri, 25 Aug 2017 10:59:20 -0700 (PDT) From: "Rodney W. Grimes" <freebsd@pdx.rh.CN85.dnsmgr.net> To: Warner Losh <imp@bsdimp.com> Cc: Slawa Olhovchenkov <slw@zxy.spb.ru>, Warner Losh <imp@freebsd.org>, src-committers <src-committers@freebsd.org>, "svn-src-all@freebsd.org" <svn-src-all@freebsd.org>, "svn-src-head@freebsd.org" <svn-src-head@freebsd.org> Subject: Re: svn commit: r322863 - head/sys/cam Message-ID: <201708251759.v7PHxKPD070178@pdx.rh.CN85.dnsmgr.net> In-Reply-To: <CANCZdfq3_BMbLm=Aua2yKYTv5VYwtBaxzBrPtwT0_Lfw=7r4sA@mail.gmail.com>
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[ Charset UTF-8 unsupported, converting... ] > On Fri, Aug 25, 2017 at 7:35 AM, Slawa Olhovchenkov <slw@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@freebsd.org
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