linux-kernel - Re: [PATCH] mpt2sas: don't handle broadcast primitives

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Message-ID: <20130724192357.GC3641@logfs.org>
Date:	Wed, 24 Jul 2013 15:23:57 -0400
From:	Jörn Engel <joern@...fs.org>
To:	Baruch Even <baruch@...en.org>
Cc:	Nagalakshmi Nandigama <Nagalakshmi.Nandigama@....com>,
	Sreekanth Reddy <Sreekanth.Reddy@....com>,
	Support <support@....com>,
	"James E.J. Bottomley" <JBottomley@...allels.com>,
	DL-MPTFusionLinux@....com, linux-scsi <linux-scsi@...r.kernel.org>,
	linux-kernel@...r.kernel.org, mit@...estorage.com
Subject: Re: [PATCH] mpt2sas: don't handle broadcast primitives

On Wed, 24 July 2013 23:42:22 +0300, Baruch Even wrote:
> On Sat, Jul 20, 2013 at 1:11 AM, Jörn Engel <joern@...fs.org> wrote:
> > On Fri, 19 July 2013 18:06:59 -0400, Jörn Engel wrote:
> >>
> >> The handling of broadcast primitives involves
> >> _scsih_block_io_all_device(), which does what the name implies.  I have
> >> observed cases with >60s of blocking io on all devices, caused by a
> >> single bad device.  The downsides of this code are obvious, while the
> >> upsides are more elusive.
> >
> > And since this patch looks more like an April fools joke: I have
> > gathered a few machine-months of testing, including tortures that
> > specifically stress the removed codepaths.  This is a serious
> > submission and unless someone can show me a _very_ good reason for
> > keeping the deleted code, I would like to get it merged.
> 
> This would seem to cause an IO pause through the host whenever there
> is a disk removal/insertion or SES (SAS expander) change which seems
> like a bad proposition indeed. The part of the work that this code
> seems to handle is that when such a change happens something needs to
> detect the dead IOs (f.ex. surprise disk removal) but I believe that
> the SAS HBA firmware will do that internally already so I do think
> this code is needless.
> 
> The only thing I'd like not to lose is the actual notification and
> ability to log the fact that there was a broadcast notification on the
> SAS network.

I agree logging would be nice.  However my attempts to keep logging and
remove the IO pause were unsuccessful.  Apparently something inside
_scsih_sas_broadcast_primitive_event() is required to get future
events.  If someone from LSI with data sheets and understanding of the
firmware can do a better patch, I would be happy.

Jörn

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