path: root/doc
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authorEdward Shishkin <>2009-12-15 18:48:12 +0100
committerJens Axboe <>2010-04-20 09:51:52 +0200
commita8d834fbba5310cfc745aeff463e65ae200eaa8b (patch)
tree3c23a47586c05ee868d1e1c8f3afa106c7067b5c /doc
parente41bf0ffcf5a2ec016493c25737896a03bfbafba (diff)
blktrace: update blkiomon doc
Fixup for 499398. Description of problem: blkiomon does not understand the output of blktrace when working with logical volume device (it is quiet, while working with physical device it prints IO statistics as expected). BUG (or design feature?): /dev/dm-* and /dev/md* don't see BLK_TC_COMPLETE actions: /* we need an older D trace and a younger C trace */ if (t_old->bit.action & BLK_TC_ACT(BLK_TC_ISSUE) && t_young->bit.action & BLK_TC_ACT(BLK_TC_COMPLETE)) { /* matching D and C traces - update statistics */ match++; blkiomon_account(&t_old->bit, &t_young->bit); blkiomon_free_trace(t_stored); return t; } Possible solution: Update documentation. Signed-off-by: Edward Shishkin <> Signed-off-by: Jens Axboe <>
Diffstat (limited to 'doc')
1 files changed, 2 insertions, 0 deletions
diff --git a/doc/blkiomon.8 b/doc/blkiomon.8
index dbed0df..aa5ece2 100644
--- a/doc/blkiomon.8
+++ b/doc/blkiomon.8
@@ -17,6 +17,8 @@ blkiomon is a block device I/O monitor. It periodically generates per-device
request size and request latency statistics from blktrace data. It provides
histograms as well as data that can be used to calculate min, max, average
and variance. For this purpose, it consumes D and C traces read from stdin.
+Note, that this doesn't work for logical volumes, as high-level drivers
+don't see the completion of the events (C).
There are options for binary output and human-readable output to files and
stdout. Output to a message queue is supported as well.