Re: Potential "AIO / io workers" inter-worker locking issue in PG18?

Hi Andres,

I realized I simply need to run perf with 'sudo' privileges, that seems 
to work. All examples I saw omitted it, so hence the confusion.

I will attempt to capture the stall with the Italy data once I finish 
another OpenStreetMap rendering test currently running.

Marco

Op 7-10-2025 om 09:34 schreef Marco Boeringa:
> Hi Andres,
>
> That worked, I successfully booted with kernel 6.8!
>
> I can now run perf, but it emits a warning, see below. Do you have 
> suggestions of how to set these perf 'paranoid' settings?
>
> Marco
>
> |Access to performance monitoring and observability operations is 
> limited.  │
> │Consider adjusting /proc/sys/kernel/perf_event_paranoid setting to 
> open    │
> │access to performance monitoring and observability operations for 
> processes│
> |without CAP_PERFMON, CAP_SYS_PTRACE or CAP_SYS_ADMIN Linux capability.
> │More information can be found at 'Perf events and tool security' 
> document: │
> │https://www.kernel.org/doc/html/latest/admin-guide/perf-security.html 
>   │
> │perf_event_paranoid setting is 4:           │
> │  -1: Allow use of (almost) all events by all users           │
> |      Ignore mlock limit after perf_event_mlock_kb without 
> CAP_IPC_LOCK    │
> │>= 0: Disallow raw and ftrace function tracepoint access        │
> │>= 1: Disallow CPU event access             │
> │>= 2: Disallow kernel profiling             │
> │To make the adjusted perf_event_paranoid setting permanent preserve 
> it     │
> │in /etc/sysctl.conf (e.g. kernel.perf_event_paranoid = <setting>)
>
> Op 7-10-2025 om 09:15 schreef Marco Boeringa:
>> It didn't work: as soon as I attempted to run perf, it emitted the 
>> warning message about the kernel version mismatch with suggestions of 
>> package to install.
>>
>> However, I now realized after further digging, that Ubuntu usually 
>> has multiple kernel versions installed. I have now attempted to add 
>> the GRUB boot menu, which should allow me to boot with the older 6.8 
>> version of the kernel (which was available during configuration of 
>> GRUB), and hopefully run perf with that version of the kernel.
>>
>> Marco
>>
>> Op 6-10-2025 om 23:39 schreef Andres Freund:
>>> On 2025-10-06 22:41:31 +0200, Marco Boeringa wrote:
>>>> Hi Andres,
>>>>
>>>> I now found out that I do have a 'perf' living under one of 'usr' 
>>>> folders,
>>>> but unfortunately, this is the 6.8 kernel version:
>>>>
>>>> /usr/lib/linux-tools-6.8.0-85
>>>>
>>>> None of the other suggested packages and their likely install 
>>>> folders seem
>>>> to contain perf.
>>>>
>>>> Since perf appears and rather understandably seems to need to 
>>>> exactly match
>>>> the kernel version, I can't use this one, as my kernel was already 
>>>> upgraded
>>>> to 6.14 by a more or less forced update in Software Updater.
>>> I'm pretty sure that you can use any halfway-recent perf binary, 
>>> they don't
>>> actually need to match exactly. I don't know why ubuntu insists on a 
>>> perfect
>>> match. I regularly run completely different versions.
>>>
>>> Greetings,
>>>
>>> Andres Freund