On Sat, Feb 15, 2025 at 10:01:13AM -0800, David Reaver wrote: > diff --git a/Documentation/admin-guide/iostats.rst b/Documentation/admin-guide/iostats.rst > index 609a3201fd4e..9453196ade51 100644 > --- a/Documentation/admin-guide/iostats.rst > +++ b/Documentation/admin-guide/iostats.rst > @@ -2,62 +2,39 @@ > I/O statistics fields > ===================== > > -Since 2.4.20 (and some versions before, with patches), and 2.5.45, > -more extensive disk statistics have been introduced to help measure disk > -activity. Tools such as ``sar`` and ``iostat`` typically interpret these and do > -the work for you, but in case you are interested in creating your own > -tools, the fields are explained here. > - > -In 2.4 now, the information is found as additional fields in > -``/proc/partitions``. In 2.6 and upper, the same information is found in two > -places: one is in the file ``/proc/diskstats``, and the other is within > -the sysfs file system, which must be mounted in order to obtain > -the information. Throughout this document we'll assume that sysfs > -is mounted on ``/sys``, although of course it may be mounted anywhere. > -Both ``/proc/diskstats`` and sysfs use the same source for the information > -and so should not differ. > - > -Here are examples of these different formats:: > - > - 2.4: > - 3 0 39082680 hda 446216 784926 9550688 4382310 424847 312726 5922052 19310380 0 3376340 23705160 > - 3 1 9221278 hda1 35486 0 35496 38030 0 0 0 0 0 38030 38030 > - > - 2.6+ sysfs: > - 446216 784926 9550688 4382310 424847 312726 5922052 19310380 0 3376340 23705160 > - 35486 38030 38030 38030 > - > - 2.6+ diskstats: > - 3 0 hda 446216 784926 9550688 4382310 424847 312726 5922052 19310380 0 3376340 23705160 > - 3 1 hda1 35486 38030 38030 38030 > - > - 4.18+ diskstats: > - 3 0 hda 446216 784926 9550688 4382310 424847 312726 5922052 19310380 0 3376340 23705160 0 0 0 0 > - > -On 2.4 you might execute ``grep 'hda ' /proc/partitions``. On 2.6+, you have > -a choice of ``cat /sys/block/hda/stat`` or ``grep 'hda ' /proc/diskstats``. > - > -The advantage of one over the other is that the sysfs choice works well > -if you are watching a known, small set of disks. ``/proc/diskstats`` may > -be a better choice if you are watching a large number of disks because > -you'll avoid the overhead of 50, 100, or 500 or more opens/closes with > -each snapshot of your disk statistics. > - > -In 2.4, the statistics fields are those after the device name. In > -the above example, the first field of statistics would be 446216. > -By contrast, in 2.6+ if you look at ``/sys/block/hda/stat``, you'll > -find just the 15 fields, beginning with 446216. If you look at > -``/proc/diskstats``, the 15 fields will be preceded by the major and > -minor device numbers, and device name. Each of these formats provides > -15 fields of statistics, each meaning exactly the same things. > -All fields except field 9 are cumulative since boot. Field 9 should > -go to zero as I/Os complete; all others only increase (unless they > -overflow and wrap). Wrapping might eventually occur on a very busy > -or long-lived system; so applications should be prepared to deal with > -it. Regarding wrapping, the types of the fields are either unsigned > -int (32 bit) or unsigned long (32-bit or 64-bit, depending on your > -machine) as noted per-field below. Unless your observations are very > -spread in time, these fields should not wrap twice before you notice it. > +The kernel exposes disk statistics via ``/proc/diskstats`` and > +``/sys/block/<device>/stat``. These stats are usually accessed via tools > +such as ``sar`` and ``iostat``. > + > +Here are examples using a disk with two partitions:: > + > + /proc/diskstats: > + 259 0 nvme0n1 255999 814 12369153 47919 996852 81 36123024 425995 0 301795 580470 0 0 0 0 60602 106555 > + 259 1 nvme0n1p1 492 813 17572 96 848 81 108288 210 0 76 307 0 0 0 0 0 0 > + 259 2 nvme0n1p2 255401 1 12343477 47799 996004 0 36014736 425784 0 344336 473584 0 0 0 0 0 0 > + > + /sys/block/nvme0n1/stat: > + 255999 814 12369153 47919 996858 81 36123056 426009 0 301809 580491 0 0 0 0 60605 106562 > + > + /sys/block/nvme0n1/nvme0n1p1/stat: > + 492 813 17572 96 848 81 108288 210 0 76 307 0 0 0 0 0 0 > + > +Both files contain the same 17 statistics. ``/sys/block/<device>/stat`` > +contains the fields for ``<device>``. In ``/proc/diskstats`` the fields > +are prefixed with the major and minor device numbers and the device > +name. In the example above, the first stat value for ``nvme0n1`` is > +255999 in both files. > + > +The sysfs ``stat`` file is efficient for monitoring a small, known set > +of disks. If you're tracking a large number of devices, > +``/proc/diskstats`` is often the better choice since it avoids the > +overhead of opening and closing multiple files for each snapshot. > + > +All fields are cumulative, monotonic counters, except for field 9, which > +resets to zero as I/Os complete. The remaining fields reset at boot, on > +device reattachment or reinitialization, or when the underlying counter > +overflows. Applications reading these counters should detect and handle > +resets when comparing stat snapshots. > > Each set of stats only applies to the indicated device; if you want > system-wide stats you'll have to find all the devices and sum them all up. > The doc LGTM, thanks! Reviewed-by: Bagas Sanjaya <bagasdotme@xxxxxxxxx> -- An old man doll... just what I always wanted! - Clara
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