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bitbake: doc: bitbake-user-manual: expand description of BB_PRESSURE_MAX variables

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(Bitbake rev: 72e9847dd578c3cbed52a9c16fea23ebbeef5046)

Signed-off-by: Paul Eggleton <paul.eggleton@microsoft.com>
Signed-off-by: Michael Opdenacker <michael.opdenacker@bootlin.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
This commit is contained in:
Michael Opdenacker
2022-10-12 15:21:20 +02:00
committed by Richard Purdie
parent fc6f743c52
commit f67176aada
1 changed files with 43 additions and 17 deletions
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bitbake/doc/bitbake-user-manual/bitbake-user-manual-ref-variables.rst
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@@ -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)