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Kernel v2.6.25-rc1 /Documentation/iostats.txt

Filename:/Documentation/iostats.txt
Lines Added:14
Lines Deleted:1
Also changed in: (Previous) 2.6.24-git22  2.6.24-git21  2.6.24-git20  2.6.24-git19  2.6.23  2.6.23-rc9 
(Following) 2.6.25-rc2  2.6.25-rc3  2.6.25-rc4  2.6.25-rc5  2.6.25-rc6  2.6.25-rc7 

Location
[  2.6.25-rc1
  [  Documentation
     o  iostats.txt

Patch

diff --git a/Documentation/iostats.txt b/Documentation/iostats.txt
index b963c3b..5925c3c 100644
--- a/Documentation/iostats.txt
+++ b/Documentation/iostats.txt
@@ -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
 ----------------
 


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