qla2xxx: Ramping down queue depth

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Environment

SUSE Linux Enterprise Server 11 Service Pack 3 (SLES 11 SP3)

Situation

In multipathed environments utilizing Qlogic HBAs, the following messages are observed:

Mar 17 13:03:46 linux kernel: [1316360.921289] qla2xxx [0000:08:00.1]-3031:4: 4:0:29: Ramping down queue depth to 16

Mar 17 13:03:46 linux kernel: [1316412.862170] qla2xxx [0000:08:00.1]-3031:4: 4:0:0: Ramping down queue depth to 8

[...]

Mar 17 13:03:47 linux kernel: [1316413.865067] qla2xxx [0000:08:00.1]-3031:4: 4:0:10: Ramping down queue depth to 4

[...]

Mar 17 13:03:47 linux kernel: [1316413.916950] qla2xxx [0000:08:00.0]-3031:3: 3:0:0: Ramping down queue depth to 9

Mar 17 13:04:13 linux kernel: [1316439.887583] qla2xxx [0000:08:00.0]-3031:3: 3:0:28: Ramping down queue depth to 4

Resolution

Cause

"Ramping down" is a qla2xxx driver feature which was introduced with SLES 11 SP3 and informs the admin of a QUEUE FULL situation on the storage side. In this case the target port on the storage array cannot cope with the I/O requests and the driver tries to lower the load by reducing the number of concurrent requests to the target.

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