Re: Debian-13 bad performance on IPC

* Franco Martelli <[email protected]>
| On 03/07/26 at 18:27, Ralf Fassel wrote:
| > - When receiving a START signal, data are stored to SSD, and an analysis
| >    program is started.  The analysis program in turn starts several
| >    sub-processes, which in turn start several sub-sub-processes.
| >    All sub-sub-processes read the recorded data files in a "tail -f" fashion.
>
| I suspect hardware issue with your IPC, maybe not all cores of the I7
| cpu are used since the IPC is fan-less.

I can see the usage of *all* 8 CPUs at full throttle when I run a
computing-intensive process like multi-channel online FFT.  This does
not degrade after several minutes, so I don't think there is physical
damage to individual CPU cores, or a overheating problem.

| Shooting in the dark, try a different scheduler, the kernel 6.12.x
| comes with three scheduler: deadline (the default), kyber and bfq. To
| see the available scheduler simply run:
>
| # cat /sys/block/sda/queue/scheduler
>
| change "sda" according to your SSD device, to try another scheduler run:
>
| # echo bfq >/sys/block/[TheSSD]/queue/scheduler

I had

  desktop% cat /sys/block/sda/queue/scheduler 
  none [mq-deadline] 

  ipc% cat /sys/block/sda/queue/scheduler 
  [none] mq-deadline

(note the different position of the [])

So I tried
  # echo mq-deadline >/sys/block/[TheSSD]/queue/scheduler
which then resulted in 

  ipc% cat /sys/block/sda/queue/scheduler 
  none [mq-deadline]

but did not change the timing of the process.

Same result for 'bfq' and 'kyber'.
    # echo bfq >/sys/block/[TheSSD]/queue/scheduler
    ipc% cat /sys/block/sda/queue/scheduler 
    none mq-deadline [bfq]

Still clustering at 1s intervalls 2/3/4s.

The crucial point is always the delayed start of one or two of the
subprocesses, which sometimes do not start to run until the recording is
stopped (as said, it varies which of the processes is starting late).

I confirmed that it is the subprocess itself which starts late (issue
timestamp right at the start), and not some processing in the subprocess
itself - the various steps in the subprocess happen very quickly once it
is running.

| If you want to know more about Linux kernel scheduler looks at
| "linux-source-6.12/Documentation/block/" directory of the kernel
| sources.

Thanks for the pointer, with that it feels somewhat less
"monkey-see-monkey-do" :-)

R'