Re: [PATCH] perf tools: Refactor precise_ip fallback logic

[Chen, Zide]

On 11/11/2025 11:34 AM, Namhyung Kim wrote:
> On Tue, Nov 11, 2025 at 11:11:45AM -0800, Chen, Zide wrote:
>>
>>
>> On 11/10/2025 11:50 PM, Namhyung Kim wrote:
>>> On Fri, Nov 07, 2025 at 02:31:23PM -0800, Chen, Zide wrote:
>>>>
>>>>
>>>> On 11/7/2025 1:42 PM, Namhyung Kim wrote:
>>>>> On Thu, Nov 06, 2025 at 05:23:09PM -0800, Chen, Zide wrote:
>>>>>>
>>>>>>
>>>>>> On 11/6/2025 10:52 AM, Namhyung Kim wrote:
> 
>>>>> Can you run these commands and show the output here?
>>>>>
>>>>>   $ perf record -e task-clock:S  true
>>>>>   $ perf evlist -v
>>>>
>>>> On 6.18.0-rc4:
>>>>
>>>> $ perf record -e task-clock:S  true
>>>> [ perf record: Woken up 2 times to write data ]
>>>> [ perf record: Captured and wrote 0.006 MB perf.data ]
>>>>
>>>> $ perf evlist -v
>>>> task-clock:Su: type: 1 (PERF_TYPE_SOFTWARE), size: 136, config: 0x1
>>>> (PERF_COUNT_SW_TASK_CLOCK), { sample_period, sample_freq }: 4000,
>>>> sample_type: IP|TID|TIME|READ|ID|PERIOD, read_format: ID|LOST, disabled:
>>>> 1, inherit: 1, exclude_kernel: 1, exclude_hv: 1, mmap: 1, comm: 1, freq:
>>>> 1, enable_on_exec: 1, task: 1, sample_id_all: 1, mmap2: 1, comm_exec: 1,
>>>> ksymbol: 1, bpf_event: 1, build_id: 1
>>>
>>> Thanks for sharing this.  Yep, it has the inherit bit.
>>>
>>> I think there's a bug in the missing feature test.  Indeed, it should
>>> also have PERF_SAMPLE_TID for the test according to the kernel comment.
>>>
>>> 	/*
>>> 	 * We do not support PERF_SAMPLE_READ on inherited events unless
>>> 	 * PERF_SAMPLE_TID is also selected, which allows inherited events to
>>> 	 * collect per-thread samples.
>>> 	 * See perf_output_read().
>>> 	 */
>>> 	if (has_inherit_and_sample_read(attr) && !(attr->sample_type & PERF_SAMPLE_TID))
>>> 		return ERR_PTR(-EINVAL);
>>
>> It seems that the purpose of the inherit_sample_read fallback is to
>> remove the inherit attribute when both PERF_SAMPLE_READ and inherit are
>> present, but PERF_SAMPLE_TID is not. The new change may not be able to
>> accomplish this?
> 
> No, the purpose of the missing feature check is to detect whether the
> current kernel supports this feature or not.  The correct check should
> pass both READ and TID together.


OK, thanks!

> Thanks,
> Namhyung
>