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[SCSI] Fix dm-multipath starvation when scsi host is busy
block congestion control doesn't have any concept of fairness across multiple queues. This means that if SCSI reports the host as busy in the queue congestion control it can result in an unfair starvation situation in dm-mp if there are multiple multipath devices on the same host. For example: http://www.redhat.com/archives/dm-devel/2012-May/msg00123.html The fix for this is to report only the sdev busy state (and ignore the host busy state) in the block congestion control call back. The host is still congested, but the SCSI subsystem will sort out the congestion in a fair way because it knows the relation between the queues and the host. [jejb: fixed up trailing whitespace] Reported-by: Bernd Schubert <bernd.schubert@itwm.fraunhofer.de> Tested-by: Bernd Schubert <bernd.schubert@itwm.fraunhofer.de> Signed-off-by: Jun'ichi Nomura <j-nomura@ce.jp.nec.com> Cc: <stable@vger.kernel.org> Signed-off-by: James Bottomley <JBottomley@Parallels.com>
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1 changed files with 7 additions and 4 deletions
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@ -1378,16 +1378,19 @@ static int scsi_lld_busy(struct request_queue *q)
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{
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struct scsi_device *sdev = q->queuedata;
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struct Scsi_Host *shost;
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struct scsi_target *starget;
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if (!sdev)
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return 0;
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shost = sdev->host;
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starget = scsi_target(sdev);
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if (scsi_host_in_recovery(shost) || scsi_host_is_busy(shost) ||
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scsi_target_is_busy(starget) || scsi_device_is_busy(sdev))
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/*
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* Ignore host/starget busy state.
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* Since block layer does not have a concept of fairness across
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* multiple queues, congestion of host/starget needs to be handled
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* in SCSI layer.
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*/
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if (scsi_host_in_recovery(shost) || scsi_device_is_busy(sdev))
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return 1;
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return 0;
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