Re: Disabling CPUs

On Wed, Sep 21, 2022 at 7:26 PM Paul Procacci <pprocacci@gmail.com> wrote:

> (Resending with list included)
>
> Hey Keith,
>
> Taken from smp(4):
>
>      FreeBSD allows specific CPUs on a multi-processor system to be
> disabled.
>      This can be done using the hint.lapic.X.disabled tunable, where X is
> the
>      APIC ID of a CPU.  Setting this tunable to 1 will result in the
>      corresponding CPU being disabled.
>
> smp(4) further describes how to detect CPU topologies and whatnot.
> Specifically the following sysctl seems useful: kern.sched.topology_spec
>
> Though I'm not entirely sure, I'd personally start with the above.
>
> ~Paul
>
> On Wed, Sep 21, 2022 at 10:06 PM Kevin Oberman <rkoberman@gmail.com>
> wrote:
>
>> I am looking to disable all 8 E-cores on my Alder Lake system to prevent
>> repeated crashes. The man page has an example of this:
>> Modify the cpuset all threads are in by default to contain only the first
>> 4 CPUs, leaving the rest idle:
>>            cpuset -l 0-3 -s 1
>> I did this, but in subsequent port build, all 12 "CPUs" were running at
>> 100%. Am I missing something? Maybe use -p 1" instead of "-s 1".
>>
>> I also found suggestions to use "hint.lapic.N.disabled", but teh lines
>> that were supposed to be in dmesg and the messages log were not present. I
>> am baffled, but really need to do something to stop the crashes currently
>> impacting Alder Lake systems.
>> --
>> Kevin Oberman, Part time kid herder and retired Network Engineer
>> E-mail: rkoberman@gmail.com
>> PGP Fingerprint: D03FB98AFA78E3B78C1694B318AB39EF1B055683
>>
>
>
> --
> __________________
>
> :(){ :|:& };:
>



Nothing looks useful in kern.sched. I am wondering if SCHED_4BSD is
impacting this. My knowledge of the schedulers is minimal, but 4BSD
provided much better responsiveness than ULE.I 've been running 4BSD on my
systems (excluding servers) for over a decade... Probably much longer. I
may try building a kernel with ULE and see what effect that has.

# sysctl kern.sched
kern.sched.runq_fuzz: 1
kern.sched.ipiwakeup.useloop: 0
kern.sched.ipiwakeup.usemask: 1
kern.sched.ipiwakeup.delivered: 26954287
kern.sched.ipiwakeup.requested: 26899799
kern.sched.ipiwakeup.enabled: 1
kern.sched.slice: 12
kern.sched.quantum: 94488
kern.sched.name: 4BSD
kern.sched.preemption: 1
kern.sched.cpusetsize: 32
-
Kevin Oberman, Part time kid herder and retired Network Engineer
E-mail: rkoberman@gmail.com
PGP Fingerprint: D03FB98AFA78E3B78C1694B318AB39EF1B055683