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SubjectRe: [RFC PATCH 0/3] md: export internal stats through debugfs
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On 7/2/19 9:29 PM, Hou Tao wrote:
> Hi,
>
> There are so many io counters, stats and flags in md, so I think
> export these info to userspace will be helpful for online-debugging,

For online-debugging, I'd suggest you have a try eBPF which can be very helpful.

-Bob

> especially when the vmlinux file and the crash utility are not
> available. And these info can also be utilized during code
> understanding.
>
> MD has already exported some stats through sysfs files under
> /sys/block/mdX/md, but using sysfs file to export more internal
> stats are not a good choice, because we need to create a single
> sysfs file for each internal stat according to the use convention
> of sysfs and there are too many internal stats. Further, the
> newly-created sysfs files would become APIs for userspace tools,
> but that is not we wanted, because these files are related with
> internal stats and internal stats may change from time to time.
>
> And I think debugfs is a better choice. Because we can show multiple
> related stats in a debugfs file, and the debugfs file will never be
> used as an userspace API.
>
> Two debugfs files are created to expose these internal stats:
> * iostat: io counters and io related stats (e.g., mddev->active_io,
> r1conf->nr_pending, or r1confi->retry_list)
> * stat: normal stats/flags (e.g., mddev->recovery, conf->array_frozen)
>
> Because internal stats are spreaded all over md-core and md-personality,
> so both md-core and md-personality will create these two debugfs files
> under different debugfs directory.
>
> Patch 1 factors out the debugfs files creation routine for md-core and
> md-personality, patch 2 creates two debugfs files: iostat & stat under
> /sys/kernel/debug/block/mdX for md-core, and patch 3 creates two debugfs
> files: iostat & stat under /sys/kernel/debug/block/mdX/raid1 for md-raid1.
>
> The following lines show the hierarchy and the content of these debugfs
> files for a RAID1 device:
>
> $ pwd
> /sys/kernel/debug/block/md0
> $ tree
> .
> ├── iostat
> ├── raid1
> │   ├── iostat
> │   └── stat
> └── stat
>
> $ cat iostat
> active_io 0
> sb_wait 0 pending_writes 0
> recovery_active 0
> bitmap pending_writes 0
>
> $ cat stat
> flags 0x20
> sb_flags 0x0
> recovery 0x0
>
> $ cat raid1/iostat
> retry_list active 0
> bio_end_io_list active 0
> pending_bio_list active 0 cnt 0
> sync_pending 0
> nr_pending 0
> nr_waiting 0
> nr_queued 0
> barrier 0
>
> $ cat raid1/stat
> array_frozen 0
>
> I'm not sure whether the division of internal stats is appropriate and
> whether the internal stats in debugfs files are sufficient, so questions
> and comments are weclome.
>
> Regards,
> Tao
>
> Hou Tao (3):
> md-debugfs: add md_debugfs_create_files()
> md: export inflight io counters and internal stats in debugfs
> raid1: export inflight io counters and internal stats in debugfs
>
> drivers/md/Makefile | 2 +-
> drivers/md/md-debugfs.c | 35 ++++++++++++++++++
> drivers/md/md-debugfs.h | 16 +++++++++
> drivers/md/md.c | 65 ++++++++++++++++++++++++++++++++++
> drivers/md/md.h | 1 +
> drivers/md/raid1.c | 78 +++++++++++++++++++++++++++++++++++++++++
> drivers/md/raid1.h | 1 +
> 7 files changed, 197 insertions(+), 1 deletion(-)
> create mode 100644 drivers/md/md-debugfs.c
> create mode 100644 drivers/md/md-debugfs.h
>

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