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Diffstat (limited to 'documentation/ref-manual/variables.rst')
-rw-r--r-- | documentation/ref-manual/variables.rst | 27 |
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diff --git a/documentation/ref-manual/variables.rst b/documentation/ref-manual/variables.rst index 9909622d7a..147679400f 100644 --- a/documentation/ref-manual/variables.rst +++ b/documentation/ref-manual/variables.rst | |||
@@ -530,6 +530,33 @@ system and gives an overview of their function and contents. | |||
530 | ":ref:`dev-manual/common-tasks:speeding up a build`" | 530 | ":ref:`dev-manual/common-tasks:speeding up a build`" |
531 | section in the Yocto Project Development Tasks Manual. | 531 | section in the Yocto Project Development Tasks Manual. |
532 | 532 | ||
533 | On the other hand, if your goal is to limit the amount of system | ||
534 | resources consumed by BitBake tasks, setting :term:`BB_NUMBER_THREADS` | ||
535 | to a number lower than the number of CPU threads in your machine | ||
536 | won't be sufficient. That's because each package will still be built | ||
537 | and installed through a number of parallel jobs specified by the | ||
538 | :term:`PARALLEL_MAKE` variable, which is by default the number of CPU | ||
539 | threads in your system, and is not impacted by the | ||
540 | :term:`BB_NUMBER_THREADS` value. | ||
541 | |||
542 | So, if you set :term:`BB_NUMBER_THREADS` to "1" but don't set | ||
543 | :term:`PARALLEL_MAKE`, most of your system resources will be consumed | ||
544 | anyway. | ||
545 | |||
546 | Therefore, if you intend to reduce the load of your build system by | ||
547 | setting :term:`BB_NUMBER_THREADS` to a relatively low value compared | ||
548 | to the number of CPU threads on your system, you should also set | ||
549 | :term:`PARALLEL_MAKE` to a similarly low value. | ||
550 | |||
551 | An alternative to using :term:`BB_NUMBER_THREADS` to keep the usage | ||
552 | of build system resources under control is to use the smarter | ||
553 | :term:`BB_PRESSURE_MAX_CPU`, :term:`BB_PRESSURE_MAX_IO` or | ||
554 | :term:`BB_PRESSURE_MAX_MEMORY` controls. They will prevent BitBake | ||
555 | from starting new tasks as long as thresholds are exceeded. Anyway, | ||
556 | as with :term:`BB_NUMBER_THREADS`, such controls won't prevent the | ||
557 | tasks already being run from using all CPU threads on the system | ||
558 | if :term:`PARALLEL_MAKE` is not set to a low value. | ||
559 | |||
533 | :term:`BB_SERVER_TIMEOUT` | 560 | :term:`BB_SERVER_TIMEOUT` |
534 | Specifies the time (in seconds) after which to unload the BitBake | 561 | Specifies the time (in seconds) after which to unload the BitBake |
535 | server due to inactivity. Set :term:`BB_SERVER_TIMEOUT` to determine how | 562 | server due to inactivity. Set :term:`BB_SERVER_TIMEOUT` to determine how |