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| author | Michael Kerrisk <mtk.manpages@gmail.com> | 2017-05-22 14:01:33 +0200 |
|---|---|---|
| committer | Michael Kerrisk <mtk.manpages@gmail.com> | 2017-05-22 14:01:33 +0200 |
| commit | e0a73a311f2cd628e1780d3567ddf0531e303211 (patch) | |
| tree | cd3532f1b4e8c045923eb5e25fb963d3c79c3712 | |
| parent | 3d5ea0476dbca2f126312eca6c42543f4fd18fec (diff) | |
| download | man-pages-e0a73a311f2cd628e1780d3567ddf0531e303211.tar.gz | |
proc.5: Document that 'iowait' field of /proc/stat is unreliable
Text taken from Chao Fan's kernel commit 9c240d757658a3ae996.
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
| -rw-r--r-- | man5/proc.5 | 16 |
1 files changed, 16 insertions, 0 deletions
diff --git a/man5/proc.5 b/man5/proc.5 index c0782d1c43..d6032e1858 100644 --- a/man5/proc.5 +++ b/man5/proc.5 @@ -3730,6 +3730,22 @@ pseudo-file. .TP .IR iowait " (since Linux 2.5.41)" (5) Time waiting for I/O to complete. +This value is not reliable, for the following reasons: +.\" See kernel commit 9c240d757658a3ae9968dd309e674c61f07c7f48 +.RS +.IP 1. 3 +The CPU will not wait for I/O to complete; +iowait is the time that a task is waiting for I/O to complete. +When a CPU goes into idle state for outstanding task I/O, +another task will be scheduled on this CPU. +.IP 2. +On a multi-core CPU, +the task waiting for I/O to complete is not running on any CPU, +so the iowait of each CPU is difficult to calculate. +.IP 3. +The value in this field may +.I decrease +in certain conditions. .TP .IR irq " (since Linux 2.6.0-test4)" (6) Time servicing interrupts. |