Merge tag 'docs-4.10' of git://git.lwn.net/linux

[mirror_ubuntu-zesty-kernel.git] / Documentation / filesystems / proc.txt

diff --git a/Documentation/filesystems/proc.txt b/Documentation/filesystems/proc.txt
index 74329fd0add2237a848a72fb71a46d5e4e98cee4..72624a16b79284c0f2484741144e6b90ac084064 100644 (file)
--- a/Documentation/filesystems/proc.txt
+++ b/Documentation/filesystems/proc.txt
@@ -191,6 +191,7 @@ read the file /proc/PID/status:
   CapPrm: 0000000000000000
   CapEff: 0000000000000000
   CapBnd: ffffffffffffffff
+  NoNewPrivs:     0
   Seccomp:        0
   voluntary_ctxt_switches:        0
   nonvoluntary_ctxt_switches:     1
@@ -262,6 +263,7 @@ Table 1-2: Contents of the status files (as of 4.1)
  CapPrm                      bitmap of permitted capabilities
  CapEff                      bitmap of effective capabilities
  CapBnd                      bitmap of capabilities bounding set
+ NoNewPrivs                  no_new_privs, like prctl(PR_GET_NO_NEW_PRIV, ...)
  Seccomp                     seccomp mode, like prctl(PR_GET_SECCOMP, ...)
  Cpus_allowed                mask of CPUs on which this process may run
  Cpus_allowed_list           Same as previous, but in "list format"
@@ -1305,7 +1307,16 @@ second).  The meanings of the columns are as follows, from left to right:
 - nice: niced processes executing in user mode
 - system: processes executing in kernel mode
 - idle: twiddling thumbs
-- iowait: waiting for I/O to complete
+- iowait: In a word, iowait stands for waiting for I/O to complete. But there
+  are several problems:
+  1. Cpu will not wait for I/O to complete, iowait is the time that a task is
+     waiting for I/O to complete. When cpu goes into idle state for
+     outstanding task io, another task will be scheduled on this CPU.
+  2. In 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.
+  3. The value of iowait field in /proc/stat will decrease in certain
+     conditions.
+  So, the iowait is not reliable by reading from /proc/stat.
 - irq: servicing interrupts
 - softirq: servicing softirqs
 - steal: involuntary wait