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Diffstat (limited to 'Documentation')
| -rw-r--r-- | Documentation/cpusets.txt | 50 |
1 files changed, 4 insertions, 46 deletions
diff --git a/Documentation/cpusets.txt b/Documentation/cpusets.txt index ef83b2dd0cb..9e49b1c3572 100644 --- a/Documentation/cpusets.txt +++ b/Documentation/cpusets.txt @@ -16,9 +16,8 @@ CONTENTS: 1.3 How are cpusets implemented ? 1.4 What are exclusive cpusets ? 1.5 What does notify_on_release do ? - 1.6 What is a marker_pid ? - 1.7 What is memory_pressure ? - 1.8 How do I use cpusets ? + 1.6 What is memory_pressure ? + 1.7 How do I use cpusets ? 2. Usage Examples and Syntax 2.1 Basic Usage 2.2 Adding/removing cpus @@ -178,7 +177,6 @@ containing the following files describing that cpuset: - mem_exclusive flag: is memory placement exclusive? - tasks: list of tasks (by pid) attached to that cpuset - notify_on_release flag: run /sbin/cpuset_release_agent on exit? - - marker_pid: pid of user task in co-ordinated operation sequence - memory_pressure: measure of how much paging pressure in cpuset In addition, the root cpuset only has the following file: @@ -260,47 +258,7 @@ boot is disabled (0). The default value of other cpusets at creation is the current value of their parents notify_on_release setting. -1.6 What is a marker_pid ? --------------------------- - -The marker_pid helps manage cpuset changes safely from user space. - -The interface presented to user space for cpusets uses system wide -numbering of CPUs and Memory Nodes. It is the responsibility of -user level code, presumably in a library, to present cpuset-relative -numbering to applications when that would be more useful to them. - -However if a task is moved to a different cpuset, or if the 'cpus' or -'mems' of a cpuset are changed, then we need a way for such library -code to detect that its cpuset-relative numbering has changed, when -expressed using system wide numbering. - -The kernel cannot safely allow user code to lock kernel resources. -The kernel could deliver out-of-band notice of cpuset changes by -such mechanisms as signals or usermodehelper callbacks, however -this can't be synchronously delivered to library code linked in -applications without intruding on the IPC mechanisms available to -the app. The kernel could require user level code to do all the work, -tracking the cpuset state before and during changes, to verify no -unexpected change occurred, but this becomes an onerous task. - -The "marker_pid" cpuset field provides a simple way to make this task -less onerous on user library code. A task writes its pid to a cpusets -"marker_pid" at the start of a sequence of queries and updates, -and check as it goes that the cpusets marker_pid doesn't change. -The pread(2) system call does a seek and read in a single call. -If the marker_pid changes, the user code should retry the required -sequence of operations. - -Anytime that a task modifies the "cpus" or "mems" of a cpuset, -unless it's pid is in the cpusets marker_pid field, the kernel zeros -this field. - -The above was inspired by the load linked and store conditional -(ll/sc) instructions in the MIPS II instruction set. - - -1.7 What is memory_pressure ? +1.6 What is memory_pressure ? ----------------------------- The memory_pressure of a cpuset provides a simple per-cpuset metric of the rate that the tasks in a cpuset are attempting to free up in @@ -357,7 +315,7 @@ the tasks in the cpuset, in units of reclaims attempted per second, times 1000. -1.8 How do I use cpusets ? +1.7 How do I use cpusets ? -------------------------- In order to minimize the impact of cpusets on critical kernel |