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-rw-r--r-- | doc/bitbake-user-manual/bitbake-user-manual-ref-variables.rst | 60 |
1 files changed, 43 insertions, 17 deletions
diff --git a/doc/bitbake-user-manual/bitbake-user-manual-ref-variables.rst b/doc/bitbake-user-manual/bitbake-user-manual-ref-variables.rst index 725e6c2cd..3522d2b77 100644 --- a/doc/bitbake-user-manual/bitbake-user-manual-ref-variables.rst +++ b/doc/bitbake-user-manual/bitbake-user-manual-ref-variables.rst @@ -484,29 +484,55 @@ overview of their function and contents. for it to work. :term:`BB_PRESSURE_MAX_CPU` - The threshold for maximum CPU pressure before BitBake prevents the - scheduling of new tasks. Once the :term:`BB_PRESSURE_MAX_CPU` threshold - is exceeded, new tasks are not started until the pressure subsides to - below the threshold. If :term:`BB_PRESSURE_MAX_CPU` is not set, CPU - pressure is not monitored. A threshold can be set in ``conf/local.conf`` - as:: + Specifies a maximum CPU pressure threshold, above which BitBake's + scheduler will not start new tasks (providing there is at least + one active task). If no value is set, CPU pressure is not + monitored when starting tasks. + + The pressure data is calculated based upon what Linux kernels since + version 4.20 expose under ``/proc/pressure``. The threshold represents + the difference in "total" pressure from the previous second. The + minimum value is 1.0 (extremely slow builds) and the maximum is + 1000000 (a pressure value unlikely to ever be reached). + + This threshold can be set in ``conf/local.conf`` as:: BB_PRESSURE_MAX_CPU = "500" :term:`BB_PRESSURE_MAX_IO` - The threshold for maximum IO pressure experienced before BitBake - prevents the scheduling of new tasks. The IO pressure is regulated in the - same way as :term:`BB_PRESSURE_MAX_CPU`. At this point in time, - experiments show that IO pressure tends to be short-lived and regulating - just the CPU can help to reduce it. + Specifies a maximum I/O pressure threshold, above which BitBake's + scheduler will not start new tasks (providing there is at least + one active task). If no value is set, I/O pressure is not + monitored when starting tasks. + + The pressure data is calculated based upon what Linux kernels since + version 4.20 expose under ``/proc/pressure``. The threshold represents + the difference in "total" pressure from the previous second. The + minimum value is 1.0 (extremely slow builds) and the maximum is + 1000000 (a pressure value unlikely to ever be reached). + + At this point in time, experiments show that IO pressure tends to + be short-lived and regulating just the CPU with + :term:`BB_PRESSURE_MAX_CPU` can help to reduce it. :term:`BB_PRESSURE_MAX_MEMORY` - The threshold for maximum memory pressure experienced before BitBake - prevents the scheduling of new tasks. The memory pressure is regulated in - the same way as :term:`BB_PRESSURE_MAX_CPU`. Note that any memory - pressure indicates that a system is being pushed beyond its capacity. At - this point in time, experiments show that memory pressure tends to be - short-lived and regulating just the CPU can help to reduce it. + + Specifies a maximum memory pressure threshold, above which BitBake's + scheduler will not start new tasks (providing there is at least + one active task). If no value is set, memory pressure is not + monitored when starting tasks. + + The pressure data is calculated based upon what Linux kernels since + version 4.20 expose under ``/proc/pressure``. The threshold represents + the difference in "total" pressure from the previous second. The + minimum value is 1.0 (extremely slow builds) and the maximum is + 1000000 (a pressure value unlikely to ever be reached). + + Memory pressure is experienced when time is spent swapping, + refaulting pages from the page cache or performing direct reclaim. + This is why memory pressure is rarely seen, but setting this variable + might be useful as a last resort to prevent OOM errors if they are + occurring during builds. :term:`BB_RUNFMT` Specifies the name of the executable script files (i.e. run files) |