From: Steffen Maier <maier@linux.ibm.com>
To: Greg KH <gregkh@linuxfoundation.org>
Cc: "James E . J . Bottomley" <jejb@linux.ibm.com>,
"Martin K . Petersen" <martin.petersen@oracle.com>,
linux-scsi@vger.kernel.org, linux-s390@vger.kernel.org,
Benjamin Block <bblock@linux.ibm.com>,
Heiko Carstens <heiko.carstens@de.ibm.com>,
Vasily Gorbik <gor@linux.ibm.com>,
stable@vger.kernel.org
Subject: Re: [PATCH v2] zfcp: fix reaction on bit error theshold notification with adapter close
Date: Tue, 1 Oct 2019 17:07:50 +0200 [thread overview]
Message-ID: <71b8fc68-23a8-a591-1018-f290d6e3312a@linux.ibm.com> (raw)
In-Reply-To: <20191001141408.GB3129841@kroah.com>
On 10/1/19 4:14 PM, Greg KH wrote:
> On Tue, Oct 01, 2019 at 12:49:49PM +0200, Steffen Maier wrote:
>> On excessive bit errors for the FCP channel ingress fibre path, the channel
>> notifies us. Previously, we only emitted a kernel message and a trace record.
>> Since performance can become suboptimal with I/O timeouts due to
>> bit errors, we now stop using an FCP device by default on channel
>> notification so multipath on top can timely failover to other paths.
>> A new module parameter zfcp.ber_stop can be used to get zfcp old behavior.
>
> Ugh, module parameters? This isn't the 1990's anymore :(
>
> Why not just make this a dynamic sysfs variable, that way you properly
> can set this on whatever device you want, not just "all or nothing"?
Since we can see many more (virtual) FCP devices than we want to actually use,
we defer probing. It means, we only start allocating structures and sysfs
entries on setting an FCP "online" for the first time. Setting online works
through another sysfs attribute owned by our ccw bus code component called
"cio". IIRC, setting online does not emit a uevent. On setting online, the
(add) uevent of hot-/coldplug of an FCP device had already happened, so we
could not easily have end users craft udev rules to automatically/persistently
configure a new sysfs attribute (which is FCP-device-specific and appears late)
to disable the new code behavior.
Not sure if that could ever become a problem for end users: Even if we were to
write into a new sysfs attribute, the attribute only appears during setting
online so this might race with starting to actually use the FCP device with the
new default behavior and could potentially disable I/O paths before the sysfs
attribute write could become effective to disable the new behavor.
--
Mit freundlichen Gruessen / Kind regards
Steffen Maier
Linux on IBM Z Development
https://www.ibm.com/privacy/us/en/
IBM Deutschland Research & Development GmbH
Vorsitzender des Aufsichtsrats: Matthias Hartmann
Geschaeftsfuehrung: Dirk Wittkopp
Sitz der Gesellschaft: Boeblingen
Registergericht: Amtsgericht Stuttgart, HRB 243294
next prev parent reply other threads:[~2019-10-01 15:08 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-09-24 16:06 [PATCH] zfcp: fix reaction on bit error theshold notification with adapter close Steffen Maier
[not found] ` <20190925224305.00183208C3@mail.kernel.org>
2019-09-26 11:00 ` Steffen Maier
2019-10-01 3:49 ` Martin K. Petersen
2019-10-01 10:49 ` [PATCH v2] " Steffen Maier
2019-10-01 14:14 ` Greg KH
2019-10-01 15:07 ` Steffen Maier [this message]
2019-10-01 15:42 ` Greg KH
2019-10-01 18:26 ` Martin K. Petersen
2019-10-02 8:31 ` Steffen Maier
2019-10-04 1:47 ` Martin K. Petersen
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