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. Thanks. [snipped] -- Coly Li
