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Date: Thu, 30 May 2024 13:54:42 +0100
From: James Clark <james.clark@....com>
To: Namhyung Kim <namhyung@...nel.org>, Ben Gainey <Ben.Gainey@....com>
Cc: "alexander.shishkin@...ux.intel.com"
<alexander.shishkin@...ux.intel.com>,
"peterz@...radead.org" <peterz@...radead.org>,
"acme@...nel.org" <acme@...nel.org>, "mingo@...hat.com" <mingo@...hat.com>,
"adrian.hunter@...el.com" <adrian.hunter@...el.com>,
"irogers@...gle.com" <irogers@...gle.com>,
"jolsa@...nel.org" <jolsa@...nel.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"linux-perf-users@...r.kernel.org" <linux-perf-users@...r.kernel.org>,
Mark Rutland <Mark.Rutland@....com>
Subject: Re: [PATCH v6 4/4] tools/perf: Allow inherit + PERF_SAMPLE_READ when
opening events
On 29/05/2024 20:18, Namhyung Kim wrote:
> Hello,
>
> On Wed, May 29, 2024 at 10:48 AM Ben Gainey <Ben.Gainey@....com> wrote:
>>
>> On Mon, 2024-05-27 at 18:47 +0100, Ben Gainey wrote:
>>> On Thu, 2024-05-23 at 18:41 -0700, Namhyung Kim wrote:
>>>> On Tue, May 21, 2024 at 6:30 AM Ben Gainey <ben.gainey@....com>
>>>> wrote:
>>>>>
>>>>> The tool will now default to this new mode if the user specifies
>>>>> a
>>>>> sampling group when not in system-wide mode, and when --no-
>>>>> inherit
>>>>> is not specified.
>>>>>
>>>>> This change updates evsel to allow the combination of inherit
>>>>> and PERF_SAMPLE_READ.
>>>>>
>>>>> A fallback is implemented for kernel versions where this feature
>>>>> is
>>>>> not
>>>>> supported.
>>>>
>>>> But I'm afraid the test would fail on old kernels. Maybe we need
>>>> to
>>>> put it in the selftests.
>>>>
>>>
>>> Sorry, not clear what you mean?
>>>
>>> Is the issue that the fallback on older kernels fails, or that the
>>> "perf test" tests fail?
>>>
>>> Thanks
>>> Ben
>>
>> Just to follow up, I've rechecked the fallback on an unmodified 6.9.1
>> kernel with the following:
>>
>> perf record -vv -e '{cycles,instructions}:S' ls
>>
>> With an unpatched version of perf running on an unpatched kernel, the
>> cycles event is opened as:
>>
>> ------------------------------------------------------------
>> perf_event_attr:
>> type 0 (PERF_TYPE_HARDWARE)
>> size 136
>> config 0 (PERF_COUNT_HW_CPU_CYCLES)
>> { sample_period, sample_freq } 4000
>> sample_type IP|TID|TIME|READ|ID|PERIOD
>> read_format ID|GROUP|LOST
>> disabled 1
>> exclude_kernel 1
>> exclude_hv 1
>> mmap 1
>> comm 1
>> freq 1
>> enable_on_exec 1
>> task 1
>> sample_id_all 1
>> exclude_guest 1
>> mmap2 1
>> comm_exec 1
>> ksymbol 1
>> bpf_event 1
>> ------------------------------------------------------------
>>
>> whereas with these patches applied to perf, on an unpatched kernel, the
>> output is as follows
>>
>> ------------------------------------------------------------
>> perf_event_attr:
>> type 0 (PERF_TYPE_HARDWARE)
>> size 136
>> config 0 (PERF_COUNT_HW_CPU_CYCLES)
>> { sample_period, sample_freq } 4000
>> sample_type IP|TID|TIME|READ|ID|PERIOD
>> read_format ID|GROUP|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
>> exclude_guest 1
>> mmap2 1
>> comm_exec 1
>> ksymbol 1
>> bpf_event 1
>> ------------------------------------------------------------
>> sys_perf_event_open: pid 3442954 cpu 0 group_fd -1 flags 0x8
>> sys_perf_event_open failed, error -22
>> Using PERF_SAMPLE_READ / :S modifier is not compatible with
>> inherit, falling back to no-inherit.
>> ------------------------------------------------------------
>> perf_event_attr:
>> type 0 (PERF_TYPE_HARDWARE)
>> size 136
>> config 0 (PERF_COUNT_HW_CPU_CYCLES)
>> { sample_period, sample_freq } 4000
>> sample_type IP|TID|TIME|READ|ID|PERIOD
>> read_format ID|GROUP|LOST
>> disabled 1
>> exclude_kernel 1
>> exclude_hv 1
>> mmap 1
>> comm 1
>> freq 1
>> enable_on_exec 1
>> task 1
>> sample_id_all 1
>> exclude_guest 1
>> mmap2 1
>> comm_exec 1
>> ksymbol 1
>> bpf_event 1
>> ------------------------------------------------------------
>>
>> The command falls back to the same configuration as was previously
>> used. The same is true for the instructions event.
>>
>> `perf test` fails on an unpatched kernel in "15: Setup struct
>> perf_event_attr" for the test "test-record-group-sampling1" but that is
>> surely expected for unpatched kernels?
>>
>> Is there some very-old kernel version where this would be expected to
>> succeed by accident?
>
> I don't think so but I don't want the test to fail depending on the
> kernel version. Maybe we can check the allowed combination
> first and skip the test if perf_event_open() fails. And then it can
> verify if the kernel rejects the unsupported combinations. Not
> sure if it's easy to do that in the current attr test framework.
>
> Thanks,
> Namhyung
I added the kernel version feature to the attr tests. Seems like you can
add two tests, one for before and one for after.
Search "kernel_until" in tests/attr
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