diff --git a/docs/sources/reference/commandline/cli.md b/docs/sources/reference/commandline/cli.md index da4daec88b..abe752260c 100644 --- a/docs/sources/reference/commandline/cli.md +++ b/docs/sources/reference/commandline/cli.md @@ -817,7 +817,8 @@ container at any point. This is useful when you want to set up a container configuration ahead of time so that it is ready to start when you need it. -Please see the [run command](#run) section for more details. +Please see the [run command](#run) section and the [Docker run reference]( +/reference/run/) for more details. #### Examples diff --git a/docs/sources/reference/run.md b/docs/sources/reference/run.md index 5e5d21154a..f2400ecfc4 100644 --- a/docs/sources/reference/run.md +++ b/docs/sources/reference/run.md @@ -405,7 +405,9 @@ container: -m="": Memory limit (format: , where unit = b, k, m or g) -memory-swap="": Total memory limit (memory + swap, format: , where unit = b, k, m or g) - -c=0 : CPU shares (relative weight) + -c, --cpu-shares=0 CPU shares (relative weight) + +### Memory constraints We have four ways to set memory usage: - memory=inf, memory-swap=inf (not specify any of them) @@ -423,35 +425,40 @@ We have four ways to set memory usage: It is not allowed to use more than L bytes of memory, swap *plus* memory usage is limited by S. -The operator can modify the priority of this container with -the `-c` option. By default, all containers run at the same priority -and get the same proportion of CPU cycles, the value specified must be 2 -or higher, if you are not setting `-c` or `--cpu-shares`, the default -shares of CPU time would be 1024. +### CPU share constraint -CPU shares is kind of CPU bandwidth weight, the proportion will only -reflect when CPU-intensive processes are running. When tasks in one -container are idle, other containers are allowed to borrow the left-over -CPU time. +By default, all containers get the same proportion of CPU cycles. This proportion +can be modified by changing the container's CPU share weighting relative +to the weighting of all other running containers. -The actual amount of CPU time can very depending on the number of containers -running on the system. If a container have a share of 1024 and two other -containers have share of 512, when processes in all containers attempt to -use 100% of CPU, the first container would receive 50% of all CPU time, if -another container with share of 1024 is added, the first container would -only get 33% of the CPU (the rest receive 16.5%, 16.5% and 33% of CPU). +To modify the proportion from the default of 1024, use the `-c` or `--cpu-shares` +flag to set the weighting to 2 or higher. -Note that shares of CPU time are distributed per all CPU cores on multi-core -systems. Even if a container is limited to less than 100% of CPU time, it -may use 100% of each individual CPU core. E.g., if we start {C0} container -with (`-c` = 512) and {C1} with (`-c` = 1024), we start three CPU-intensive -processes (one in {C0} and two in {C1}) on a system with more than three -cores, might results in the following division of CPU shares: +The proportion will only apply when CPU-intensive processes are running. +When tasks in one container are idle, other containers can use the +left-over CPU time. The actual amount of CPU time will vary depending on +the number of containers running on the system. -PID container CPU CPU share -100 {C0} 0 100% of CPU0 -101 {C1} 1 100% of CPU1 -102 {C1} 2 100% of CPU2 +For example, consider three containers, one has a cpu-share of 1024 and +two others have a cpu-share setting of 512. When processes in all three +containers attempt to use 100% of CPU, the first container would receive +50% of the total CPU time. If you add a fouth container with a cpu-share +of 1024, the first container only gets 33% of the CPU. The remaining containers +receive 16.5%, 16.5% and 33% of the CPU. + +On a multi-core system, the shares of CPU time are distributed over all CPU +cores. Even if a container is limited to less than 100% of CPU time, it can +use 100% of each individual CPU core. + +For example, consider a system with more than three cores. If you start one +container `{C0}` with `-c=512` running one process, and another container +`{C1}` with `-c=1024` running two processes, this can result in the following +division of CPU shares: + + PID container CPU CPU share + 100 {C0} 0 100% of CPU0 + 101 {C1} 1 100% of CPU1 + 102 {C1} 2 100% of CPU2 ## Runtime privilege, Linux capabilities, and LXC configuration