linux-kernel - Re: Interrupts are being dropped under heavy IO on -rt .

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Date:	Thu, 23 Apr 2009 14:38:31 -0700
From:	jvrao <jvrao@...ux.vnet.ibm.com>
To:	Andrew Vasquez <andrew.vasquez@...gic.com>
CC:	LKML <linux-kernel@...r.kernel.org>,
	rt-users <linux-rt-users@...r.kernel.org>,
	Mike Anderson <andmike@...ux.vnet.ibm.com>,
	"Luis Claudio R. Goncalves" <lgoncalv@...hat.com>,
	Linux Driver <Linux-Driver@...gic.com>
Subject: Re: Interrupts are being dropped under heavy IO on -rt .

Andrew Vasquez wrote:
> 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)?

Hi, the following link provides more information on the logs and our analysis.

https://bugzilla.redhat.com/show_bug.cgi?id=466903

[root@...3c29 R2-SR1]# lspci | grep -i qlogic
03:05.0 Fibre Channel: QLogic Corp. ISP2422-based 4Gb Fibre Channel to PCI-X HBA (rev 02)
03:05.1 Fibre Channel: QLogic Corp. ISP2422-based 4Gb Fibre Channel to PCI-X HBA (rev 02)


Storage is DS4700 (Product ID: 1814)

If you need more information, please let me know, I can generate more information/logs.
I will also find time to reproduce this with ql2xextended_error_logging enabled.

Thanks,
JV

> 
> Regards,
> Andrew Vasquez
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