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authorLinus Torvalds <torvalds@linux-foundation.org>2017-07-15 21:58:58 +0200
committerLinus Torvalds <torvalds@linux-foundation.org>2017-07-15 21:58:58 +0200
commit486088bc4689f826b80aa317b45ac9e42e8b25ee (patch)
treeadf5847a6119d24da990d9e336f005c4a316e6be /Documentation/iostats.txt
parentMerge tag 'random_for_linus' of git://git.kernel.org/pub/scm/linux/kernel/git... (diff)
parentdocs: kprobes.txt: Fix whitespacing (diff)
downloadlinux-486088bc4689f826b80aa317b45ac9e42e8b25ee.tar.xz
linux-486088bc4689f826b80aa317b45ac9e42e8b25ee.zip
Merge tag 'standardize-docs' of git://git.lwn.net/linux
Pull documentation format standardization from Jonathan Corbet: "This series converts a number of top-level documents to the RST format without incorporating them into the Sphinx tree. The hope is to bring some uniformity to kernel documentation and, perhaps more importantly, have our existing docs serve as an example of the desired formatting for those that will be added later. Mauro has gone through and fixed up a lot of top-level documentation files to make them conform to the RST format, but without moving or renaming them in any way. This will help when we incorporate the ones we want to keep into the Sphinx doctree, but the real purpose is to bring a bit of uniformity to our documentation and let the top-level docs serve as examples for those writing new ones" * tag 'standardize-docs' of git://git.lwn.net/linux: (84 commits) docs: kprobes.txt: Fix whitespacing tee.txt: standardize document format cgroup-v2.txt: standardize document format dell_rbu.txt: standardize document format zorro.txt: standardize document format xz.txt: standardize document format xillybus.txt: standardize document format vfio.txt: standardize document format vfio-mediated-device.txt: standardize document format unaligned-memory-access.txt: standardize document format this_cpu_ops.txt: standardize document format svga.txt: standardize document format static-keys.txt: standardize document format smsc_ece1099.txt: standardize document format SM501.txt: standardize document format siphash.txt: standardize document format sgi-ioc4.txt: standardize document format SAK.txt: standardize document format rpmsg.txt: standardize document format robust-futexes.txt: standardize document format ...
Diffstat (limited to 'Documentation/iostats.txt')
-rw-r--r--Documentation/iostats.txt76
1 files changed, 45 insertions, 31 deletions
diff --git a/Documentation/iostats.txt b/Documentation/iostats.txt
index 65f694f2d1c9..04d394a2e06c 100644
--- a/Documentation/iostats.txt
+++ b/Documentation/iostats.txt
@@ -1,49 +1,50 @@
+=====================
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
+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, the same information is found in two
-places: one is in the file /proc/diskstats, and the other is within
+``/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
+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:
+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
+ 2.4:
+ 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 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
-2.6 diskstats:
- 3 0 hda 446216 784926 9550688 4382310 424847 312726 5922052 19310380 0 3376340 23705160
- 3 1 hda1 35486 38030 38030 38030
+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``.
-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
+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
+By contrast, in 2.6+ if you look at ``/sys/block/hda/stat``, you'll
find just the eleven fields, beginning with 446216. If you look at
-/proc/diskstats, the eleven fields will be preceded by the major and
+``/proc/diskstats``, the eleven fields will be preceded by the major and
minor device numbers, and device name. Each of these formats provides
eleven fields of statistics, each meaning exactly the same things.
All fields except field 9 are cumulative since boot. Field 9 should
@@ -59,30 +60,40 @@ system-wide stats you'll have to find all the devices and sum them all up.
Field 1 -- # of reads completed
This is the total number of reads completed successfully.
+
Field 2 -- # of reads merged, field 6 -- # of writes merged
Reads and writes which are adjacent to each other may be merged for
efficiency. Thus two 4K reads may become one 8K read before it is
ultimately handed to the disk, and so it will be counted (and queued)
as only one I/O. This field lets you know how often this was done.
+
Field 3 -- # of sectors read
This is the total number of sectors read successfully.
+
Field 4 -- # of milliseconds spent reading
This is the total number of milliseconds spent by all reads (as
measured from __make_request() to end_that_request_last()).
+
Field 5 -- # of writes completed
This is the total number of writes completed successfully.
+
Field 6 -- # of writes merged
See the description of field 2.
+
Field 7 -- # of sectors written
This is the total number of sectors written successfully.
+
Field 8 -- # of milliseconds spent writing
This is the total number of milliseconds spent by all writes (as
measured from __make_request() to end_that_request_last()).
+
Field 9 -- # of I/Os currently in progress
The only field that should go to zero. Incremented as requests are
given to appropriate struct request_queue and decremented as they finish.
+
Field 10 -- # of milliseconds spent doing I/Os
This field increases so long as field 9 is nonzero.
+
Field 11 -- weighted # of milliseconds spent doing I/Os
This field is incremented at each I/O start, I/O completion, I/O
merge, or read of these stats by the number of I/Os in progress
@@ -97,7 +108,7 @@ introduced when changes collide, so (for instance) adding up all the
read I/Os issued per partition should equal those made to the disks ...
but due to the lack of locking it may only be very close.
-In 2.6, there are counters for each CPU, which make the lack of locking
+In 2.6+, there are counters for each CPU, which make the lack of locking
almost a non-issue. When the statistics are read, the per-CPU counters
are summed (possibly overflowing the unsigned long variable they are
summed to) and the result given to the user. There is no convenient
@@ -106,22 +117,25 @@ user interface for accessing the per-CPU counters themselves.
Disks vs Partitions
-------------------
-There were significant changes between 2.4 and 2.6 in the I/O subsystem.
+There were significant changes between 2.4 and 2.6+ in the I/O subsystem.
As a result, some statistic information disappeared. The translation from
a disk address relative to a partition to the disk address relative to
the host disk happens much earlier. All merges and timings now happen
at the disk level rather than at both the disk and partition level as
-in 2.4. Consequently, you'll see a different statistics output on 2.6 for
+in 2.4. Consequently, you'll see a different statistics output on 2.6+ for
partitions from that for disks. There are only *four* fields available
-for partitions on 2.6 machines. This is reflected in the examples above.
+for partitions on 2.6+ machines. This is reflected in the examples above.
Field 1 -- # of reads issued
This is the total number of reads issued to this partition.
+
Field 2 -- # of sectors read
This is the total number of sectors requested to be read from this
partition.
+
Field 3 -- # of writes issued
This is the total number of writes issued to this partition.
+
Field 4 -- # of sectors written
This is the total number of sectors requested to be written to
this partition.
@@ -149,16 +163,16 @@ to some (probably insignificant) inaccuracy.
Additional notes
----------------
-In 2.6, sysfs is not mounted by default. If your distribution of
+In 2.6+, sysfs is not mounted by default. If your distribution of
Linux hasn't added it already, here's the line you'll want to add to
-your /etc/fstab:
+your ``/etc/fstab``::
-none /sys sysfs defaults 0 0
+ none /sys sysfs defaults 0 0
-In 2.6, all disk statistics were removed from /proc/stat. In 2.4, they
-appear in both /proc/partitions and /proc/stat, although the ones in
-/proc/stat take a very different format from those in /proc/partitions
+In 2.6+, all disk statistics were removed from ``/proc/stat``. In 2.4, they
+appear in both ``/proc/partitions`` and ``/proc/stat``, although the ones in
+``/proc/stat`` take a very different format from those in ``/proc/partitions``
(see proc(5), if your system has it.)
-- ricklind@us.ibm.com