On 2023-04-06 23:07, Chen Qi via lists.openembedded.org wrote:
> According to kernel PSI doc[1], for /proc/pressure/* interface files,
> the first line is the 'some' line and the second line is the 'full'
> line.
>
> Quoting from the doc:
> """
> The "some" line indicates the share of time in which at least some tasks
> are stalled on a given resource.
>
> The "full" line indicates the share of time in which all non-idle tasks
> are stalled on a given resource simultaneously. In this state actual CPU
> cycles are going to waste, and a workload that spends extended time in this
> state is considered to be thrashing. This has severe impact on performance,
> and it’s useful to distinguish this situation from a state where some tasks
> are stalled but the CPU is still doing productive work.
> """
>
> We can see that the 'full' line is a better measurement to check if things are
> slowed down as a whole.
>
> Also, the /proc/pressure/cpu's 'full' line may not be available on some systems,
> so fall back to the 'some' line.
>
> [1]https://www.kernel.org/doc/html/latest/accounting/psi.html

NACK...

I'd need to dig up or reproduce some test cases but I believe that
we should NOT use 'full' instead of 'some'. We want to have a *lower* 
threshold

to defer work when the system resources are experiencing pressure.
We don't want to wait for the system to get to a state where all of the
resources are under pressure.


There may be use cases involving containers where the 'full' PSI info
is more useful or even essential but need a motivating example.


../Randy

>
> Signed-off-by: Chen Qi<Qi.Chen@windriver.com>
> ---
>   bitbake/lib/bb/runqueue.py | 23 +++++++++++++++--------
>   1 file changed, 15 insertions(+), 8 deletions(-)
>
> diff --git a/bitbake/lib/bb/runqueue.py b/bitbake/lib/bb/runqueue.py
> index 02f1474540..e3198dcdeb 100644
> --- a/bitbake/lib/bb/runqueue.py
> +++ b/bitbake/lib/bb/runqueue.py
> @@ -173,10 +173,13 @@ class RunQueueScheduler(object):
>                   with open("/proc/pressure/cpu") as cpu_pressure_fds, \
>                       open("/proc/pressure/io") as io_pressure_fds, \
>                       open("/proc/pressure/memory") as memory_pressure_fds:
> -
> -                    self.prev_cpu_pressure = cpu_pressure_fds.readline().split()[4].split("=")[1]
> -                    self.prev_io_pressure = io_pressure_fds.readline().split()[4].split("=")[1]
> -                    self.prev_memory_pressure = memory_pressure_fds.readline().split()[4].split("=")[1]
> +                    cpu_lines = cpu_pressure_fds.readlines()
> +                    if len(cpu_lines) == 1:
> +                        self.prev_cpu_pressure = cpu_lines[0].split()[4].split("=")[1]
> +                    else:
> +                        self.prev_cpu_pressure = cpu_lines[1].split()[4].split("=")[1]
> +                    self.prev_io_pressure = io_pressure_fds.readlines()[1].split()[4].split("=")[1]
> +                    self.prev_memory_pressure = memory_pressure_fds.readlines()[1].split()[4].split("=")[1]
>                       self.prev_pressure_time = time.time()
>                   self.check_pressure = True
>               except:
> @@ -194,10 +197,14 @@ class RunQueueScheduler(object):
>               with open("/proc/pressure/cpu") as cpu_pressure_fds, \
>                   open("/proc/pressure/io") as io_pressure_fds, \
>                   open("/proc/pressure/memory") as memory_pressure_fds:
> -                # extract "total" from /proc/pressure/{cpu|io}
> -                curr_cpu_pressure = cpu_pressure_fds.readline().split()[4].split("=")[1]
> -                curr_io_pressure = io_pressure_fds.readline().split()[4].split("=")[1]
> -                curr_memory_pressure = memory_pressure_fds.readline().split()[4].split("=")[1]
> +                # extract "total" from /proc/pressure/{cpu|io|memory}
> +                cpu_lines = cpu_pressure_fds.readlines()
> +                if len(cpu_lines) == 1:
> +                    curr_cpu_pressure = cpu_lines[0].split()[4].split("=")[1]
> +                else:
> +                    curr_cpu_pressure = cpu_lines[1].split()[4].split("=")[1]
> +                curr_io_pressure = io_pressure_fds.readlines()[1].split()[4].split("=")[1]
> +                curr_memory_pressure = memory_pressure_fds.readlines()[1].split()[4].split("=")[1]
>                   now = time.time()
>                   tdiff = now - self.prev_pressure_time
>                   if tdiff > 1.0:
>
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-- 
# Randy MacLeod
# Wind River Linux