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Commit 0e53c2be authored by Jerome Marchand's avatar Jerome Marchand Committed by Jens Axboe
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Enhanced partition statistics: documentation update 



Update the documentation to reflect the change in userspace interface.

Signed-off-by: default avatarJerome Marchand <jmarchan@redhat.com>
Signed-off-by: default avatarJens Axboe <jens.axboe@oracle.com>
parent c3c930d9

Documentation/ABI/testing/procfs-diskstats

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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

Documentation/ABI/testing/sysfs-block

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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.

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

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