On Mon, 24 Nov 2025 09:14:57 -0800, Paul E. McKenney wrote:
> On Mon, Nov 24, 2025 at 06:10:56PM +0900, Akira Yokosawa wrote:
>> Hi Paul,
>>
>> I see a couple of minor issues in running
>>
>> - make cross-klitmus; cd klitmus; make
>> - make run-herd7
>>
>> under CodeSamples/formal/herd/.
>>
>> This patch set should resolve those issues.
>
> Queued and pushed, thank you!
Paul, this is a side note with regard to klitmus7.
In the old days with Linux kernel <6.0, tests listed in KLITMUS_READY
took less than a minute.
That have changed a lot. Litmus tests with RCU primitives tend to
take much longer.
In the list of processes shown by "top", such klitmus threads are
accompanied by a single (and fairly busy) "rcu_exp_gp_kthread_worker".
Yes, the frequency RCU primitives are invoked in those litmus tests,
especially synchronize_rcu(), is unusually high. In realistic workloads,
such burst of synchronize_rcu()s would indicate you are doing something
wrong. So the longer time to complete does not mean any performance
regression.
Following is a list of summaries from C-RomanPenyaev-list-rcu-rr runs
under several VMs:
- Ubuntu 20.04 POWER8 (kernel: 5.4.0-223-generic #243-Ubuntu SMP, 8 CPUs)
Hash=890796f9231134fff935fc64b2b98940
Observation C-RomanPenyaev-list-rcu-rr Never 0 4000000
Time C-RomanPenyaev-list-rcu-rr 17.85
no rcu_exp_gp_kthread_worker.
- Ubuntu 24.04 POWER9 (kernel: 6.8.0-88-generic #89-Ubuntu SMP, 8 CPUs)
Hash=890796f9231134fff935fc64b2b98940
Observation C-RomanPenyaev-list-rcu-rr Never 0 4000000
Time C-RomanPenyaev-list-rcu-rr 153.49
no rcu_exp_gp_kthread_worker observed.
- Ubuntu 24.04 x86_64 (kernel: 6.8.0-88-generic #89-Ubuntu SMP PREEMPT_DYNAMIC,
6 CPUs)
Hash=890796f9231134fff935fc64b2b98940
Observation C-RomanPenyaev-list-rcu-rr Never 0 3000000
Time C-RomanPenyaev-list-rcu-rr 60.46
no rcu_exp_gp_kthread_worker.
- Ubuntu 25.10 x86_64 (kernel: 6.17.0-7-generic #7-Ubuntu SMP PREEMPT_DYNAMIC,
6 CPUs)
Hash=890796f9231134fff935fc64b2b98940
Observation C-RomanPenyaev-list-rcu-rr Never 0 3000000
Time C-RomanPenyaev-list-rcu-rr 311.79
rcu_exp_gp_kthread_worker consumes a lot of time.
- Fedora 43 x86_64 (kernel: 6.17.8-300.fc43.x86_64 #1 SMP PREEMPT_DYNAMIC, 6
CPUs)
Hash=890796f9231134fff935fc64b2b98940
Observation C-RomanPenyaev-list-rcu-rr Never 0 3000000
Time C-RomanPenyaev-list-rcu-rr 326.54
rcu_exp_gp_kthread_worker consumes a lot of time.
Just out of curiosity, is there any knob I can tweak to reduce the time
to complete, preferably some kernel boot arg?
Thanks, Akira
