> -----Original Message----- > From: linux-kernel-owner@xxxxxxxxxxxxxxx <linux-kernel- > owner@xxxxxxxxxxxxxxx> On Behalf Of Jens Axboe > Sent: Monday, February 11, 2019 8:50 PM > To: James Bottomley <James.Bottomley@xxxxxxxxxxxxxxxxxxxxx>; Mikael > Pettersson <mikpelinux@xxxxxxxxx> > Cc: Linux SPARC Kernel Mailing List <sparclinux@xxxxxxxxxxxxxxx>; > linux-block@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; linux-scsi > <linux-scsi@xxxxxxxxxxxxxxx> > Subject: Re: [5.0-rc5 regression] "scsi: kill off the legacy IO path" > causes 5 minute delay during boot on Sun Blade 2500 ... > > We can either fix this by setting the QUEUE_FLAG_ADD_RANDOM if > > there's no 0xB1 page or by setting the default as Jens proposed. > > I'd recommend just doing my patch, since that'll be the same behavior > that SCSI had before. When blk-mq and scsi-mq were introduced to boost SAS SSDs over 1 million IOPS, this was purposely kept off, because it generated a noticeable 3-12 us latency blip whenever the "fast_mix" code ran out of bits. If Jens' patch changes the default to be enabled for all scsi-mq users, that'll be a change for the newer legacy scsi-mq users (except for users that don't trust the default and always set the value in sysfs).
