On Tue, 25 Jun 2019, Coly Li wrote:
On 2019/6/25 2:14 上午, Eric Wheeler wrote:Hi Coli,
On Mon, 24 Jun 2019, Coly Li wrote:Hi Eric,
On 2019/6/23 7:16 上午, Eric Wheeler wrote:Perhaps they do not set stripe_width using io_opt? I did a grep to see if
From: Eric Wheeler <git@xxxxxxxxxxxxxxxxxx>Hi Eric,
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>
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.
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.
Maybe bumping version makes sense, but even if you do not, this is safe toYes, I understand you, it works as you suggested. I need to think how to
use on systems without bumping the version because the values are unused
and default to 0.
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.
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?