Message ID | 20221012124304.2926858-1-michael.opdenacker@bootlin.com |
---|---|
State | New |
Headers | show |
Series | doc: bitbake-user-manual: expand description of BB_PRESSURE_MAX variables | expand |
Hi Michael, Paul, On 10/12/22 14:43, Michael Opdenacker via lists.yoctoproject.org wrote: > From: Michael Opdenacker <michael.opdenacker@bootlin.com> > > Signed-off-by: Paul Eggleton <paul.eggleton@microsoft.com> > Signed-off-by: Michael Opdenacker <michael.opdenacker@bootlin.com> > --- > .../bitbake-user-manual-ref-variables.rst | 60 +++++++++++++------ > 1 file 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 725e6c2c..b9c1b75d 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 (recent) Linux "recent" does not mean much. Can we remove this or get a minimal version number? Cheers, Quentin
Hi Quentin, On 10/12/22 14:52, Quentin Schulz via lists.yoctoproject.org wrote: > Hi Michael, Paul, > > On 10/12/22 14:43, Michael Opdenacker via lists.yoctoproject.org wrote: >> From: Michael Opdenacker <michael.opdenacker@bootlin.com> >> >> Signed-off-by: Paul Eggleton <paul.eggleton@microsoft.com> >> Signed-off-by: Michael Opdenacker <michael.opdenacker@bootlin.com> >> --- >> .../bitbake-user-manual-ref-variables.rst | 60 +++++++++++++------ >> 1 file 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 725e6c2c..b9c1b75d 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 (recent) Linux > > "recent" does not mean much. Can we remove this or get a minimal > version number? Very good point! /proc/pressure was introduced in Linux 4.20 (https://kernelnewbies.org/Linux_4.20#Pressure_stall_information_for_better_overview_of_system_load) I'm sending an update soon. Thanks again Michael.
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 725e6c2c..b9c1b75d 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 (recent) Linux + kernels 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 (recent) Linux + kernels 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 (recent) Linux + kernels 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)