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Enhanced partition statistics: documentation update

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Update the documentation to reflect the change in userspace interface.

Signed-off-by: Jerome Marchand <jmarchan@redhat.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
This commit is contained in:
Jerome Marchand 2008-02-08 11:10:56 +01:00 committed by Jens Axboe
parent c3c930d933
commit 0e53c2be04
3 changed files with 64 additions and 1 deletions
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22
Documentation/ABI/testing/procfs-diskstats Normal file
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@ -0,0 +1,22 @@
What: /proc/diskstats
Date: February 2008
Contact: Jerome Marchand <jmarchan@redhat.com>
Description:
The /proc/diskstats file displays the I/O statistics
of block devices. Each line contains the following 14
fields:
1 - major number
2 - minor mumber
3 - device name
4 - reads completed succesfully
5 - reads merged
6 - sectors read
7 - time spent reading (ms)
8 - writes completed
9 - writes merged
10 - sectors written
11 - time spent writing (ms)
12 - I/Os currently in progress
13 - time spent doing I/Os (ms)
14 - weighted time spent doing I/Os (ms)
For more details refer to Documentation/iostats.txt

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Documentation/ABI/testing/sysfs-block Normal file
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What: /sys/block/<disk>/stat
Date: February 2008
Contact: Jerome Marchand <jmarchan@redhat.com>
Description:
The /sys/block/<disk>/stat files displays the I/O
statistics of disk <disk>. They contain 11 fields:
1 - reads completed succesfully
2 - reads merged
3 - sectors read
4 - time spent reading (ms)
5 - writes completed
6 - writes merged
7 - sectors written
8 - time spent writing (ms)
9 - I/Os currently in progress
10 - time spent doing I/Os (ms)
11 - weighted time spent doing I/Os (ms)
For more details refer Documentation/iostats.txt
What: /sys/block/<disk>/<part>/stat
Date: February 2008
Contact: Jerome Marchand <jmarchan@redhat.com>
Description:
The /sys/block/<disk>/<part>/stat files display the
I/O statistics of partition <part>. The format is the
same as the above-written /sys/block/<disk>/stat
format.

15
Documentation/iostats.txt
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@ -58,7 +58,7 @@ they should not wrap twice before you notice them.
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.
Field 1 -- # of reads issued
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
@ -132,6 +132,19 @@ words, the number of reads for partitions is counted slightly before time
of queuing for partitions, and at completion for whole disks. This is
a subtle distinction that is probably uninteresting for most cases.
More significant is the error induced by counting the numbers of
reads/writes before merges for partitions and after for disks. Since a
typical workload usually contains a lot of successive and adjacent requests,
the number of reads/writes issued can be several times higher than the
number of reads/writes completed.
In 2.6.25, the full statistic set is again available for partitions and
disk and partition statistics are consistent again. Since we still don't
keep record of the partition-relative address, an operation is attributed to
the partition which contains the first sector of the request after the
eventual merges. As requests can be merged across partition, this could lead
to some (probably insignificant) innacuracy.
Additional notes
----------------