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

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Date:	Wed, 24 Jul 2013 23:42:22 +0300
From:	Baruch Even <baruch@...en.org>
To:	Jörn Engel <joern@...fs.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 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.

Baruch
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