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bitbake: doc: bitbake-user-manual-ref-variables: improve BB_PRESSURE_* doc

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The current default value for BB_PRESSURE_MAX_CPU is 500, which is
really low for most systems. Provide a value of 15000 which limits the
load average without being extremely slow either.

Provide similar values for BB_PRESSURE_MAX_IO and
BB_PRESSURE_MAX_MEMORY. Mention that these should be adjusted depending
on the need, and warn about the potential spam of messages when the
value is too low.

(Bitbake rev: 09baa527dafca4bdf56a9189f6b3f7512886cbfb)

Signed-off-by: Antonin Godard <antonin.godard@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
This commit is contained in:
Antonin Godard 2025-06-24 14:25:02 +02:00 committed by Richard Purdie
parent e9754adb05
commit 3546e9d522
1 changed files with 64 additions and 6 deletions
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70
bitbake/doc/bitbake-user-manual/bitbake-user-manual-ref-variables.rst
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@ -538,11 +538,28 @@ overview of their function and contents.
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).
1000000 (a pressure value unlikely to ever be reached). See
https://docs.kernel.org/accounting/psi.html for more information.
This threshold can be set in ``conf/local.conf`` as::
A default value to limit the CPU pressure to be set in ``conf/local.conf``
could be::
BB_PRESSURE_MAX_CPU = "500"
BB_PRESSURE_MAX_CPU = "15000"
Multiple values should be tested on the build host to determine what suits
best, depending on the need for performances versus load average during
the build.
.. note::
You may see numerous messages printed by BitBake in the case the
:term:`BB_PRESSURE_MAX_CPU` is too low:
Pressure status changed to CPU: True, IO: False, Mem: False (CPU: 1105.9/2.0, IO: 0.0/2.0, Mem: 0.0/2.0) - using 1/64 bitbake threads
This means that the :term:`BB_PRESSURE_MAX_CPU` should be increased to
a reasonable value for limiting the CPU pressure on the system.
Monitor the varying value after ``IO:`` above to set a sensible value.
:term:`BB_PRESSURE_MAX_IO`
Specifies a maximum I/O pressure threshold, above which BitBake's
@ -554,14 +571,34 @@ overview of their function and contents.
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).
1000000 (a pressure value unlikely to ever be reached). See
https://docs.kernel.org/accounting/psi.html for more information.
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`
A default value to limit the IO pressure to be set in ``conf/local.conf``
could be::
BB_PRESSURE_MAX_IO = "15000"
Multiple values should be tested on the build host to determine what suits
best, depending on the need for performances versus I/O usage during the
build.
.. note::
You may see numerous messages printed by BitBake in the case the
:term:`BB_PRESSURE_MAX_IO` is too low::
Pressure status changed to CPU: None, IO: True, Mem: False (CPU: 2236.0/None, IO: 153.6/2.0, Mem: 0.0/2.0) - using 19/64 bitbake threads
This means that the :term:`BB_PRESSURE_MAX_IO` should be increased to
a reasonable value for limiting the I/O pressure on the system.
Monitor the varying value after ``IO:`` above to set a sensible value.
:term:`BB_PRESSURE_MAX_MEMORY`
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
@ -571,7 +608,8 @@ overview of their function and contents.
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).
1000000 (a pressure value unlikely to ever be reached). See
https://docs.kernel.org/accounting/psi.html for more information.
Memory pressure is experienced when time is spent swapping,
refaulting pages from the page cache or performing direct reclaim.
@ -579,6 +617,26 @@ overview of their function and contents.
might be useful as a last resort to prevent OOM errors if they are
occurring during builds.
A default value to limit the memory pressure to be set in
``conf/local.conf`` could be::
BB_PRESSURE_MAX_MEMORY = "15000"
Multiple values should be tested on the build host to determine what suits
best, depending on the need for performances versus memory consumption
during the build.
.. note::
You may see numerous messages printed by BitBake in the case the
:term:`BB_PRESSURE_MAX_MEMORY` is too low::
Pressure status changed to CPU: None, IO: False, Mem: True (CPU: 29.5/None, IO: 0.0/2.0, Mem: 2553.3/2.0) - using 17/64 bitbake threads
This means that the :term:`BB_PRESSURE_MAX_MEMORY` should be increased to
a reasonable value for limiting the memory pressure on the system.
Monitor the varying value after ``Mem:`` above to set a sensible value.
:term:`BB_RUNFMT`
Specifies the name of the executable script files (i.e. run files)
saved into ``${``\ :term:`T`\ ``}``. By default, the