linux-kernel - Re: [PATCH v3] tracing: Support to dump instance traces by ftrace_dump_on

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Date: Tue, 23 Jan 2024 18:23:58 +0800
From: Huang Yiwei <quic_hyiwei@...cinc.com>
To: Steven Rostedt <rostedt@...dmis.org>
CC: <mhiramat@...nel.org>, <mark.rutland@....com>, <mcgrof@...nel.org>,
        <keescook@...omium.org>, <j.granados@...sung.com>,
        <mathieu.desnoyers@...icios.com>, <corbet@....net>,
        <linux-kernel@...r.kernel.org>, <linux-trace-kernel@...r.kernel.org>,
        <linux-fsdevel@...r.kernel.org>, <linux-doc@...r.kernel.org>,
        <quic_bjorande@...cinc.com>, <quic_tsoni@...cinc.com>,
        <quic_satyap@...cinc.com>, <quic_aiquny@...cinc.com>,
        <kernel@...cinc.com>, Ross Zwisler <zwisler@...gle.com>,
        Joel Fernandes <joel@...lfernandes.org>
Subject: Re: [PATCH v3] tracing: Support to dump instance traces by
 ftrace_dump_on_oops



On 1/20/2024 12:56 AM, Steven Rostedt wrote:
> On Fri, 19 Jan 2024 16:08:24 +0800
> Huang Yiwei <quic_hyiwei@...cinc.com> wrote:
> 
>> -	ftrace_dump_on_oops[=orig_cpu]
>> +	ftrace_dump_on_oops[=orig_cpu | =<instance>]
> 
> I wonder if we should have it be:
> 
> 	ftrace_dump_on_oops[=orig_cpu | =<instance> | =<instance>:orig_cpu ]
> 
> Then last would be to only print out a specific CPU trace of the given instance.
> 
> And if we really want to be fancy!
> 
> 	ftrace_dump_on_opps[=orig_cpu | =<instance> | =orig_cpu:<instance> ][,<instance> | ,<instance>:orig_cpu]
> 
Yeah, I agree to make the parameter more flexible.

"=orig_cpu:<instance>" means to dump global and another instance?

I'm thinking of the following format:

ftrace_dump_on_opps[=orig_cpu | =<instance>][,<instance> | 
,<instance>=orig_cpu]

Here list some possible situations:

1. Dump global on orig_cpu:
ftrace_dump_on_oops=orig_cpu

2. Dump global and instance1 on all cpu, instance2 on orig_cpu:
ftrace_dump_on_opps,<instance1>,<instance2>=orig_cpu

3. Dump global and instance1 on orig_cpu, instance2 on all cpu:
ftrace_dump_on_opps=orig_cpu,<instance1>=orig_cpu,<instance2>

4. Dump instance1 on all cpu, instance2 on orig_cpu:
ftrace_dump_on_opps=<instance1>,<instance2>=orig_cpu

5. Dump instance1 and instance2 on orig_cpu:
ftrace_dump_on_opps=<instance1>=orig_cpu,<instance2>=orig_cpu

This makes orig_cpu dump for global same as instance, the parameter may 
seems more unified and users don't need to remember another markers to 
request orig_cpu dump.

But one problem here is if there's an instance named "orig_cpu", then we 
may not dump it correctly.

Regards,
Huang Yiwei

> That would allow dumping more than one instance.
> 
> If you want to dump the main buffer and an instance foo:
> 
> 	ftrace_dump_on_opps,foo
> 
> Where the ',' says to dump the top instance as well as the foo instance.
> 
> -- Steve
> 
> 
>>   			[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
>> +			If no parameter is passed, ftrace will dump global
>> +			buffers of all CPUs, if you pass orig_cpu, it will
>>   			dump only the buffer of the CPU that triggered the
>> -			oops.
>> +			oops, or specific instance will be dumped if instance
>> +			name is passed.
>>