On 05/22/2012 02:54 PM, Mike Snitzer wrote: > On Tue, May 22 2012 at 5:57am -0400, > Jun'ichi Nomura <j-nomura@xxxxxxxxxxxxx> wrote: > >> On 05/22/12 18:13, James Bottomley wrote: >>> Isn't a more understandable explanation: >> >> Thank you. That's quite elegant. >> I replaced the description with it. >> >>> And please put a comment in the code as well otherwise someone will >>> eventually send a "fix" for this because we're not paying attention to >>> host busy (and I'll have forgotten about the issue by then and might >>> apply it). >> >> Added the comment in code. >> >>> A final note is that this is more a band aid than a fix because this is >>> still a congestion situation dm-mp should be aware of. >> >> Yes. To do that, we have to generalize the concept of "host" >> and share it with block layer. >> >> Attached below is the revised patch. >> >> ---------------------------------------------------------- >> [PATCH v2] 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. >> >> Reported-by: Bernd Schubert <bernd.schubert@xxxxxxxxxxxxxxxxxx> >> Tested-by: Bernd Schubert <bernd.schubert@xxxxxxxxxxxxxxxxxx> >> Signed-off-by: Jun'ichi Nomura <j-nomura@xxxxxxxxxxxxx> >> Cc: James Bottomley <James.Bottomley@xxxxxxxxxxxxxxxxxxxxx> >> Cc: Mike Snitzer <snitzer@xxxxxxxxxx> > > Acked-by: Mike Snitzer <snitzer@xxxxxxxxxx> > Acked-by: Hannes Reinecke <hare@xxxxxxx> Cheers, Hannes -- Dr. Hannes Reinecke zSeries & Storage hare@xxxxxxx +49 911 74053 688 SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg GF: J. Hawn, J. Guild, F. Imendörffer, HRB 16746 (AG Nürnberg) -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
