X-Git-Url: http://pilppa.org/gitweb/gitweb.cgi?a=blobdiff_plain;f=Documentation%2Fiostats.txt;h=59a69ec67c408a54ee724df4d4a64a69a8317f68;hb=1f6d6e8ebe73ba9d9d4c693f7f6f50f661dbd6e4;hp=b963c3b4afa5e65b538d53d43e277e3ee7290727;hpb=0de085bb474f64e4fdb2f1ff3268590792648c7b;p=linux-2.6-omap-h63xx.git

diff --git a/Documentation/iostats.txt b/Documentation/iostats.txt
index b963c3b4afa..59a69ec67c4 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) inaccuracy.
+
 Additional notes
 ----------------