From a8d834fbba5310cfc745aeff463e65ae200eaa8b Mon Sep 17 00:00:00 2001 From: Edward Shishkin Date: Tue, 15 Dec 2009 18:48:12 +0100 Subject: [PATCH] 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 --- doc/blkiomon.8 | 2 ++ 1 file changed, 2 insertions(+) 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. -- 2.25.1