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Commit 378012cf authored by Mauro Carvalho Chehab's avatar Mauro Carvalho Chehab Committed by Jonathan Corbet
Browse files

iostats.txt: standardize document format 



Each text file under Documentation follows a different
format. Some doesn't even have titles!

Change its representation to follow the adopted standard,
using ReST markups for it to be parseable by Sphinx:

- promote main title level;
- mark literal blocks as such;
- Add blank lines to avoid Sphinx errors.

Signed-off-by: default avatarMauro Carvalho Chehab <mchehab@s-opensource.com>
Signed-off-by: default avatarJonathan Corbet <corbet@lwn.net>
parent 0e95c853

Documentation/iostats.txt

+27 −13
Original line number Original line Diff line number Diff line 
=====================

I/O statistics fields

I/O statistics fields

---------------

=====================





Since 2.4.20 (and some versions before, with patches), and 2.5.45,

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

more extensive disk statistics have been introduced to help measure disk
@@ -16,7 +17,7 @@ is mounted on /sys, although of course it may be mounted anywhere. 
Both /proc/diskstats and sysfs use the same source for the information

Both /proc/diskstats and sysfs use the same source for the information

and so should not differ.

and so should not differ.





Here are examples of these different formats:

Here are examples of these different formats::





   2.4:

   2.4:

      3     0   39082680 hda 446216 784926 9550688 4382310 424847 312726 5922052 19310380 0 3376340 23705160

      3     0   39082680 hda 446216 784926 9550688 4382310 424847 312726 5922052 19310380 0 3376340 23705160
@@ -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

Field  1 -- # of reads completed

    This is the total number of reads completed successfully.

    This is the total number of reads completed successfully.



Field  2 -- # of reads merged, field 6 -- # of writes merged

Field  2 -- # of reads merged, field 6 -- # of writes merged

    Reads and writes which are adjacent to each other may be merged for

    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

    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)

    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.

    as only one I/O.  This field lets you know how often this was done.



Field  3 -- # of sectors read

Field  3 -- # of sectors read

    This is the total number of sectors read successfully.

    This is the total number of sectors read successfully.



Field  4 -- # of milliseconds spent reading

Field  4 -- # of milliseconds spent reading

    This is the total number of milliseconds spent by all reads (as

    This is the total number of milliseconds spent by all reads (as

    measured from __make_request() to end_that_request_last()).

    measured from __make_request() to end_that_request_last()).



Field  5 -- # of writes completed

Field  5 -- # of writes completed

    This is the total number of writes completed successfully.

    This is the total number of writes completed successfully.



Field  6 -- # of writes merged

Field  6 -- # of writes merged

    See the description of field 2.

    See the description of field 2.



Field  7 -- # of sectors written

Field  7 -- # of sectors written

    This is the total number of sectors written successfully.

    This is the total number of sectors written successfully.



Field  8 -- # of milliseconds spent writing

Field  8 -- # of milliseconds spent writing

    This is the total number of milliseconds spent by all writes (as

    This is the total number of milliseconds spent by all writes (as

    measured from __make_request() to end_that_request_last()).

    measured from __make_request() to end_that_request_last()).



Field  9 -- # of I/Os currently in progress

Field  9 -- # of I/Os currently in progress

    The only field that should go to zero. Incremented as requests are

    The only field that should go to zero. Incremented as requests are

    given to appropriate struct request_queue and decremented as they finish.

    given to appropriate struct request_queue and decremented as they finish.



Field 10 -- # of milliseconds spent doing I/Os

Field 10 -- # of milliseconds spent doing I/Os

    This field increases so long as field 9 is nonzero.

    This field increases so long as field 9 is nonzero.



Field 11 -- weighted # of milliseconds spent doing I/Os

Field 11 -- weighted # of milliseconds spent doing I/Os

    This field is incremented at each I/O start, I/O completion, I/O

    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

    merge, or read of these stats by the number of I/Os in progress
@@ -117,11 +128,14 @@ for partitions on 2.6 machines. This is reflected in the examples above. 




Field  1 -- # of reads issued

Field  1 -- # of reads issued

    This is the total number of reads issued to this partition.

    This is the total number of reads issued to this partition.



Field  2 -- # of sectors read

Field  2 -- # of sectors read

    This is the total number of sectors requested to be read from this

    This is the total number of sectors requested to be read from this

    partition.

    partition.



Field  3 -- # of writes issued

Field  3 -- # of writes issued

    This is the total number of writes issued to this partition.

    This is the total number of writes issued to this partition.



Field  4 -- # of sectors written

Field  4 -- # of sectors written

    This is the total number of sectors requested to be written to

    This is the total number of sectors requested to be written to

    this partition.

    this partition.
@@ -151,7 +165,7 @@ 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

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