On Tue, 25 Jun 2019, Coly Li wrote: > On 2019/6/25 2:14 上午, Eric Wheeler wrote: > > On Mon, 24 Jun 2019, Coly Li wrote: > > > >> On 2019/6/23 7:16 上午, Eric Wheeler wrote: > >>> From: Eric Wheeler <git@xxxxxxxxxxxxxxxxxx> > >>> > >>> While some drivers set queue_limits.io_opt (e.g., md raid5), there are > >>> currently no SCSI/RAID controller drivers that do. Previously stripe_size > >>> and partial_stripes_expensive were read-only values and could not be > >>> tuned by users (eg, for hardware RAID5/6). > >>> > >>> This patch enables users to save the optimal IO size via sysfs through > >>> the backing device attributes stripe_size and partial_stripes_expensive > >>> into the bcache superblock. > >>> > >>> Superblock changes are backwards-compatable: > >>> > >>> * partial_stripes_expensive: One bit was used in the superblock flags field > >>> > >>> * stripe_size: There are eight 64-bit "pad" fields for future use in > >>> the superblock which default to 0; from those, 32-bits are now used > >>> to save the stripe_size and load at device registration time. > >>> > >>> Signed-off-by: Eric Wheeler <bcache@xxxxxxxxxxxxxxxxxx> > >> > >> Hi Eric, > >> > >> In general I am OK with this patch. Since Peter comments lots of SCSI > >> RAID devices reports a stripe width, could you please list the hardware > >> raid devices which don't list stripe size ? Then we can make decision > >> whether it is necessary to have such option enabled. > > > > Perhaps they do not set stripe_width using io_opt? I did a grep to see if > > any of them did, but I didn't see them. How is stripe_width indicated by > > RAID controllers? > > > > If they do set io_opt, then at least my Areca 1883 does not set io_opt as > > of 4.19.x. I also have a LSI MegaRAID 3108 which does not report io_opt as > > of 4.1.x, but that is an older kernel so maybe support has been added > > since then. > > > > Martin, > > > > Where would stripe_width be configured in the SCSI drivers? Is it visible > > through sysfs or debugfs so I can check my hardware support without > > hacking debugging the kernel? > > > >> > >> Another point is, this patch changes struct cache_sb, it is no problem > >> to change on-disk format. I plan to update the super block version soon, > >> to store more configuration persistently into super block. stripe_size > >> can be added to cache_sb with other on-disk changes. > > > > Hi Eric, > > > Maybe bumping version makes sense, but even if you do not, this is safe to > > use on systems without bumping the version because the values are unused > > and default to 0. > > Yes, I understand you, it works as you suggested. I need to think how to > organize all options in struct cache_sb, stripe_size will be arranged > then. And I will ask help to you for reviewing the changes of on-disk > format. Hi Coli, Just checking in, its been a while and I didn't see any more discussion on the topic: This would benefit users with older RAID controllers using RAID-5/6 that don't set io_opt. Even new new RAID controlers that _do_ provide `io_opt` still do _not_ indicate partial_stripes_expensive (which is an mdraid feature, but Martin please correct me if I'm wrong here). Thus, all hardware RAID-5/6 users could benefit by manually flagging partial_stripes_expensive to get burst writes out of bcache that fit their stride width. This patch probably needs rebased and documentation updated about io_opt, but here is the original patch with documentation for your reference: https://lkml.org/lkml/2019/6/22/298 What do you think? -Eric > > Thanks. > > [snipped] > > -- > > Coly Li >
