Date: Wed, 15 Apr 2009 12:48:02 -0700
From: Andrew Vasquez <andrew.vasquez@qlogic.com>
To: jvrao <jvrao@linux.vnet.ibm.com>
Cc: LKML <linux-kernel@vger.kernel.org>,
       rt-users <linux-rt-users@vger.kernel.org>,
       Mike Anderson <andmike@linux.vnet.ibm.com>,
       "Luis Claudio R. Goncalves" <lgoncalv@redhat.com>,
       Linux Driver <Linux-Driver@qlogic.com>
Subject: Re: Interrupts are being dropped under heavy IO on -rt .
Message-ID: <20090415194802.GD1382@plap4-2.local>
References: <49DF71CF.7070509@linux.vnet.ibm.com>
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On Fri, 10 Apr 2009, jvrao wrote:

> Qlogic driver uses MSI-EDGE interrupts by default.
>  
> On -rt kernel under heavy IO load we observed that the driver missed 
> interrupts occasionally.
> 
> Missing interrupts caused spurious mailbox timeouts and path failovers.
> 
> Suspecting MSI interrupts, we disabled MSI and forcing the driver to use 
> APIC interrupts (Patch attached).
> 
> With this change, our IO tests ran for extended period of time without 
> any issues.
> 
> It would be interesting to see if the MSI infrastructure itself has 
> issues on realtime, or it is the combination of qla2xxx/MSI.
> 
> Right now we don't have any setup to test out MSI with other adapters. 
> Hence, wondering if anyone faced similar issues.

Could you perhaps provide some details on hardware used within your
testing -- HBA type, storage, etc?  Also, can you share any logs of
the failures with extended-error-logging enabled
(ql2xextended_error_logging)?

Regards,
Andrew Vasquez
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