Hi, On 2019/7/23 7:30, Bob Liu wrote: > 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. > Thanks for your suggestion. Using an eBPF program to read these internal status from a host which is fully under your control is a good choice, but when the dependencies of an eBPF program (e.g., the minor version of the kernel and the kernel configuration which will influence the struct layout) is out-of-your-control, it's not a good choice. Thanks, Tao > -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 >> > > > . >
