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SubjectRe: [PATCH v5] tracing: Support to dump instance traces by ftrace_dump_on_oops
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On 2/27/2024 9:47 AM, Steven Rostedt wrote:
> On Thu, 8 Feb 2024 21:18:14 +0800
> Huang Yiwei <quic_hyiwei@quicinc.com> wrote:
>
>> Currently ftrace only dumps the global trace buffer on an OOPs. For
>> debugging a production usecase, instance trace will be helpful to
>> check specific problems since global trace buffer may be used for
>> other purposes.
>>
>> This patch extend the ftrace_dump_on_oops parameter to dump a specific
>> or multiple trace instances:
>>
>> - ftrace_dump_on_oops=0: as before -- don't dump
>> - ftrace_dump_on_oops[=1]: as before -- dump the global trace buffer
>> on all CPUs
>> - ftrace_dump_on_oops=2 or =orig_cpu: as before -- dump the global
>> trace buffer on CPU that triggered the oops
>> - ftrace_dump_on_oops=<instance_name>: new behavior -- dump the
>> tracing instance matching <instance_name>
>> - ftrace_dump_on_oops[=2/orig_cpu],<instance1_name>[=2/orig_cpu],
>> <instrance2_name>[=2/orig_cpu]: new behavior -- dump the global trace
>> buffer and multiple instance buffer on all CPUs, or only dump on CPU
>> that triggered the oops if =2 or =orig_cpu is given
>
> So we need to add that the syntax is:
>
> ftrace_dump_on_oops[=[<0|1|2|orig_cpu>,][<instance_name>[=<1|2|orig_cpu>][,...]]
>
Yeah, this is much more clear, will update the commit message and kernel
docs in new patchset.
>>
>> Also, the sysctl node can handle the input accordingly.
>>
>> Cc: Ross Zwisler <zwisler@google.com>
>> Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
>> Signed-off-by: Huang Yiwei <quic_hyiwei@quicinc.com>
>> ---
>> .../admin-guide/kernel-parameters.txt | 26 ++-
>> Documentation/admin-guide/sysctl/kernel.rst | 30 +++-
>> include/linux/ftrace.h | 4 +-
>> include/linux/kernel.h | 1 +
>> kernel/sysctl.c | 4 +-
>> kernel/trace/trace.c | 156 +++++++++++++-----
>> kernel/trace/trace_selftest.c | 2 +-
>> 7 files changed, 168 insertions(+), 55 deletions(-)
>>
>> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
>> index 31b3a25680d0..3d6ea8e80c2f 100644
>> --- a/Documentation/admin-guide/kernel-parameters.txt
>> +++ b/Documentation/admin-guide/kernel-parameters.txt
>> @@ -1561,12 +1561,28 @@
>> The above will cause the "foo" tracing instance to trigger
>> a snapshot at the end of boot up.
>>
>> - ftrace_dump_on_oops[=orig_cpu]
>> + ftrace_dump_on_oops[=2(orig_cpu) | =<instance>][,<instance> |
>> + ,<instance>=2(orig_cpu)]
>> [FTRACE] will dump the trace buffers on oops.
>> - If no parameter is passed, ftrace will dump
>> - buffers of all CPUs, but if you pass orig_cpu, it will
>> - dump only the buffer of the CPU that triggered the
>> - oops.
>> + If no parameter is passed, ftrace will dump global
>> + buffers of all CPUs, if you pass 2 or orig_cpu, it
>> + will dump only the buffer of the CPU that triggered
>> + the oops, or the specific instance will be dumped if
>> + its name is passed. Multiple instance dump is also
>> + supported, and instances are separated by commas. Each
>> + instance supports only dump on CPU that triggered the
>> + oops by passing 2 or orig_cpu to it.
>> +
>> + ftrace_dump_on_oops=foo=orig_cpu
>> +
>> + The above will dump only the buffer of "foo" instance
>> + on CPU that triggered the oops.
>> +
>> + ftrace_dump_on_oops,foo,bar=orig_cpu
>
> I believe the above is incorrect. It should be:
>
> ftrace_dump_on_oops=foo,bar=orig_cpu
>
> And you can add here as well:
>
> ftrace_dump_on_oops[=[<0|1|2|orig_cpu>,][<instance_name>[=<1|2|orig_cpu>][,...]]
>
>
> Thanks,
>
> --Steve
>
The explanation is below, I think it's correct?
- "ftrace_dump_on_oops," means global buffer on all CPUs
- "foo," means foo instance on all CPUs
- "bar=orig_cpu" means bar instance on CPU that triggered the oops.

I'm trying to make the example to cover more possibilities.

Regards,
Huang Yiwei
>> +
>> + The above will dump global buffer on all CPUs, the
>> + buffer of "foo" instance on all CPUs and the buffer
>> + of "bar" instance on CPU that triggered the oops.
>>
>> ftrace_filter=[function-list]

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