Re: [PATCH] arm64: topology: Fix false warning in counters_read_on_cpu() for same-CPU reads

[Sumit Gupta <sumitg@nvidia.com>]

On 24/02/26 07:12, Jie Zhan wrote:
> External email: Use caution opening links or attachments
>
>
> On 2/24/2026 2:29 AM, Will Deacon wrote:
>> On Wed, Jan 28, 2026 at 01:04:17PM +0000, Will Deacon wrote:
>>> On Wed, Jan 28, 2026 at 06:50:42PM +0800, Jie Zhan wrote:
>>>> On 1/27/2026 4:07 PM, Sumit Gupta wrote:
>>>>> The counters_read_on_cpu() function warns when called with IRQs disabled
>>>>> to prevent deadlock in smp_call_function_single(). However, this warning
>>>>> is spurious when reading counters on the current CPU since no IPI is
>>>>> needed for same-CPU reads.
>>>>>
>>>>> Commit 12eb8f4fff24 ("cpufreq: CPPC: Update FIE arch_freq_scale in ticks
>>>>> for non-PCC regs") changed the CPPC Frequency Invariance Engine to read
>>>>> AMU counters directly from the scheduler tick for non-PCC register
>>>>> spaces (like FFH), instead of deferring to a kthread. This means
>>>>> counters_read_on_cpu() is now called with IRQs disabled from the tick
>>>>> handler, triggering the warning:
>>>>>
>>>>> | WARNING: arch/arm64/kernel/topology.c:410 at counters_read_on_cpu
>>>>> | ...
>>>>> | Call trace:
>>>>> |  counters_read_on_cpu+0x88/0xa8 (P)
>>>>> |  cpc_read_ffh+0xdc/0x148
>>>>> |  cpc_read+0x260/0x518
>>>>> |  cppc_get_perf_ctrs+0xf0/0x398
>>>>> |  __cppc_scale_freq_tick+0x4c/0x148 [cppc_cpufreq]
>>>>> |  cppc_scale_freq_tick+0x44/0x88 [cppc_cpufreq]
>>>>> |  topology_scale_freq_tick+0x34/0x58
>>>>> |  sched_tick+0x58/0x300
>>>>> |  update_process_times+0xcc/0x120
>>>>> |  tick_nohz_handler+0xa8/0x260
>>>>> |  __hrtimer_run_queues+0x154/0x360
>>>>> |  hrtimer_interrupt+0xf4/0x2b0
>>>>> |  arch_timer_handler_phys+0x4c/0x78
>>>>> |  ....
>>>>> |  CPPC Cpufreq:__cppc_scale_freq_tick: failed to read perf counters
>>>>> |  ....
>>>>>
>>>>> Fix this by calling the counter read function directly for same-CPU
>>>>> case, bypassing smp_call_function_single() entirely. Use get_cpu() to
>>>>> disable preemption as the counter read functions call this_cpu_has_cap()
>>>>> which requires a non-preemptible context.
>>>>>
>>>>> Fixes: 12eb8f4fff24 ("cpufreq: CPPC: Update FIE arch_freq_scale in ticks for non-PCC regs")
>>>>> Signed-off-by: Sumit Gupta <sumitg@nvidia.com>
>>>> Reviewed-by: Jie Zhan <zhanjie9@hisilicon.com>
>>>>
>>>> Looks fine for me except for the minor comment wrapping.
>>>>
>>>> Thanks for spotting this.
>>>> I may have missed the warning log in the FFH test.
>>>>
>>>> This happens during the short window in cpufreq_policy_online() between
>>>> driver->init() and the CREATE_POLICY notifier that gets AMU FIE ready.
>>>> After that, CPPC FIE will be stopped.
>>>>
>>>> Ideally this can be merged together with Viresh's PR since the CPPC FIE
>>>> changes are there.
>>>> https://lore.kernel.org/all/j4qdid7iqmng4gzb5ozefemjkep3wx2b5z2yki5tnqc3vzvzf4@kvrnarvdod5p/
>>> Right, looks like this should go via Rafael but if it doesn't make the merge
>>> window then I can pick it up at -rc1 (please remind me :)
>> Looks like this fix is still needed. Please can you post a new version,
>> based on -rc1, so that I can pick it up?
>>
>> You'll also need to fix the SHA in the commit message and the Fixes: tag,
>> as 12eb8f4fff24 doesn't match the upstream change.
>>
>> Will
>>
> I believe this goes to Sumit because he's the author.
>
> Sumit, can you update this patch?
>
> Jie

Sent v2[1] with updated Fixes: tag and re-based on v7.0-rc1.

[1] https://lore.kernel.org/lkml/20260224092714.1242141-1-sumitg@nvidia.com/

Thank you,
Sumit Gupta