> -----Original Message----- > From: linux-kernel-owner@xxxxxxxxxxxxxxx [mailto:linux-kernel- > owner@xxxxxxxxxxxxxxx] On Behalf Of Tejun Heo > Sent: Tuesday, 23 September, 2014 1:12 AM > To: Christoph Hellwig > Cc: Jens Axboe; linux-kernel@xxxxxxxxxxxxxxx; linux-scsi@xxxxxxxxxxxxxxx > Subject: Re: boot stall regression due to blk-mq: use percpu_ref for mq usage > count > > On Tue, Sep 23, 2014 at 08:09:06AM +0200, Christoph Hellwig wrote: > > On Tue, Sep 23, 2014 at 02:01:41AM -0400, Tejun Heo wrote: > > > On Tue, Sep 23, 2014 at 07:59:24AM +0200, Christoph Hellwig wrote: > > > > "[PATCHSET percpu/for-3.18] percpu_ref: implement > switch_to_atomic/percpu()" > > > > > > > > looks way to big for 3.17, and the regression was introduced in the > 3.17 > > > > merge window. I'm not sure what was broken before, but it defintively > > > > survived a lot of testing. > > > > > > Do we even care about fixing it for 3.17? scsi-mq isn't enabled by > > > default even for 3.18. The open-coded percpu ref thing was subtly > > > broken there. It'd be difficult to trigger but I'm fairly sure it'd > > > crap out in the wild once in a blue moon. > > > > It's compiled in by default, and people are extremly eager to test it. > > Ugh, I don't know. It's not like we have a very good baseline we can > go back to and reverting it for -stable and then redoing it seems > kinda excessive for a yet experimental feature. Jens? scsi_mod.use_blk_mq is not listed in 3.17rc6 Documentation/kernel- parameters.txt or Documentation/scsi/scsi-parameters.txt (which does admit "This document may not be entirely up to date and comprehensive."). Perhaps a description with an "experimental" warning could be slipped into scsi-parameters.txt in 3.17, with plans to remove that warning in 3.18. --- Rob Elliott HP Server Storage -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
