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Diffstat (limited to 'Documentation/cgroups')
| -rw-r--r-- | Documentation/cgroups/cpuacct.txt | 18 |
1 files changed, 18 insertions, 0 deletions
diff --git a/Documentation/cgroups/cpuacct.txt b/Documentation/cgroups/cpuacct.txt index bb775fbe43d..8b930946c52 100644 --- a/Documentation/cgroups/cpuacct.txt +++ b/Documentation/cgroups/cpuacct.txt @@ -30,3 +30,21 @@ The above steps create a new group g1 and move the current shell process (bash) into it. CPU time consumed by this bash and its children can be obtained from g1/cpuacct.usage and the same is accumulated in /cgroups/cpuacct.usage also. + +cpuacct.stat file lists a few statistics which further divide the +CPU time obtained by the cgroup into user and system times. Currently +the following statistics are supported: + +user: Time spent by tasks of the cgroup in user mode. +system: Time spent by tasks of the cgroup in kernel mode. + +user and system are in USER_HZ unit. + +cpuacct controller uses percpu_counter interface to collect user and +system times. This has two side effects: + +- It is theoretically possible to see wrong values for user and system times. + This is because percpu_counter_read() on 32bit systems isn't safe + against concurrent writes. +- It is possible to see slightly outdated values for user and system times + due to the batch processing nature of percpu_counter. |