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authorKonstantin Khlebnikov <khlebnikov@yandex-team.ru>2019-11-21 13:40:26 +0300
committerJens Axboe <axboe@kernel.dk>2019-11-21 09:06:47 -0700
commitb6866318657717c8914673a6394894d12bc9ff5e (patch)
treef4d534373b711f368f079d0cc54d3d71892e1feb /Documentation/block
parent40d47c155e8ae9bcb3f2d0d01cf14d903c664726 (diff)
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block: add iostat counters for flush requests
Requests that triggers flushing volatile writeback cache to disk (barriers) have significant effect to overall performance. Block layer has sophisticated engine for combining several flush requests into one. But there is no statistics for actual flushes executed by disk. Requests which trigger flushes usually are barriers - zero-size writes. This patch adds two iostat counters into /sys/class/block/$dev/stat and /proc/diskstats - count of completed flush requests and their total time. Signed-off-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru> Signed-off-by: Jens Axboe <axboe@kernel.dk>
Diffstat (limited to 'Documentation/block')
-rw-r--r--Documentation/block/stat.rst14
1 files changed, 12 insertions, 2 deletions
diff --git a/Documentation/block/stat.rst b/Documentation/block/stat.rst
index 9c07bc22b0bc..77311335c08b 100644
--- a/Documentation/block/stat.rst
+++ b/Documentation/block/stat.rst
@@ -41,6 +41,8 @@ discard I/Os requests number of discard I/Os processed
discard merges requests number of discard I/Os merged with in-queue I/O
discard sectors sectors number of sectors discarded
discard ticks milliseconds total wait time for discard requests
+flush I/Os requests number of flush I/Os processed
+flush ticks milliseconds total wait time for flush requests
=============== ============= =================================================
read I/Os, write I/Os, discard I/0s
@@ -48,6 +50,14 @@ read I/Os, write I/Os, discard I/0s
These values increment when an I/O request completes.
+flush I/Os
+==========
+
+These values increment when an flush I/O request completes.
+
+Block layer combines flush requests and executes at most one at a time.
+This counts flush requests executed by disk. Not tracked for partitions.
+
read merges, write merges, discard merges
=========================================
@@ -62,8 +72,8 @@ discarded from this block device. The "sectors" in question are the
standard UNIX 512-byte sectors, not any device- or filesystem-specific
block size. The counters are incremented when the I/O completes.
-read ticks, write ticks, discard ticks
-======================================
+read ticks, write ticks, discard ticks, flush ticks
+===================================================
These values count the number of milliseconds that I/O requests have
waited on this block device. If there are multiple I/O requests waiting,