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Date:      Fri, 23 Aug 2013 10:00:59 -0700
From:      Scott Long <scott4long@yahoo.com>
To:        Dmitry Morozovsky <marck@rinet.ru>
Cc:        svn-src-head@freebsd.org, svn-src-all@freebsd.org, src-committers@freebsd.org, "Kenneth D. Merry" <ken@freebsd.org>
Subject:   Re: svn commit: r254615 - head/sys/dev/mps
Message-ID:  <74108713-986A-4CBD-A441-395C7B54456A@yahoo.com>
In-Reply-To: <alpine.BSF.2.00.1308221856010.10197@woozle.rinet.ru>
References:  <201308212130.r7LLUvO5008991@svn.freebsd.org> <alpine.BSF.2.00.1308221641010.10197@woozle.rinet.ru> <20130822142107.GA49996@nargothrond.kdm.org> <alpine.BSF.2.00.1308221856010.10197@woozle.rinet.ru>

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On Aug 22, 2013, at 7:58 AM, Dmitry Morozovsky <marck@rinet.ru> wrote:

> On Thu, 22 Aug 2013, Kenneth D. Merry wrote:
>=20
>>>>  Fix mps(4) driver breakage that came in in change 253550 that
>>>>  manifested itself in out of chain frame conditions.
>>>>=20
>>>>  When the driver ran out of chain frames, the request in question
>>>>  would get completed early, and go through =
mpssas_scsiio_complete().
>=20
>>> what is real impact of the bug?
>>=20
>> Your system will essentially hang, certainly as far as anything =
connected
>> to the controller in question.
>=20
> [snip]
>=20
>> 5.  Look for an out of chain frames message on the console.  To see =
how far
>> you are towards using the chain frames, run 'sysctl dev.mps'.  You =
can see
>> how many chain frames you have free, and how many requests have =
failed.
>>=20
>> This change just needs to be merged along with the other changes to =
avoid
>> having the regression in stable.
>=20
> Thank you very much for the explanation.  We use a couple of servers =
with mps=20
> (and many spindles there), all on stable/9 from this summer, and you =
commit=20
> turns on an alarm light in my head ;)


I'll confirm with my netflix hat on that this isn't a problem in 9.

Scott




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