linux-kernel - Re: trace: multiple ring buffers

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Message-ID: <4F06AD22.3090806@hitachi.com>
Date:	Fri, 06 Jan 2012 17:13:22 +0900
From:	Hiraku TOYOOKA <hiraku.toyooka.gu@...achi.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	linux-kernel@...r.kernel.org, masami.hiramatsu.pt@...achi.com,
	yrl.pp-manager.tt@...achi.com
Subject: Re: trace: multiple ring buffers

Hello, Steven,

Thank you for your reply.

 >> Multiple buffer support makes these really easy. I'm sure that other users wish
 >> to use it. Of course, it will introduce some complexities to ftrace code.
 >
 > Not really. I've always Nack'd the making of the global_ops non-static
 > for this very reason. The events may need some work, but nothing too
 > hard.

You mentioned the global_trace instead of the global_ops, didn't you?

 > Yeah, basically I figured we create another directory inside the
 > debugfs/tracing directory. Maybe call it sub_buffers or something.
 > Inside this directory we could have:
 >
 > create_buffer - a file that you echo a name into to create a new buffer,
 > then a directory with that name will appear in this directory.
 >
 > echo foobar > debugfs/tracing/sub_buffers/create
 >
 > ls debugfs/tracing/sub_buffers/foobar
 >
 > buffer_size_kb current_tracer events set_ftrace_filter ...
 >
 > basically the new directory foobar will be a copy of the debugfs/tracing
 > directory with a few things possibly missing. Then each of these will be
 > agnostic to the main tracer.

Thank you for telling me your idea. I think this interface is nice. I'll try to
realize it.

Best regards,
Hiraku Toyooka


Steven Rostedt wrote:
> Hi Hiraku,
> 
> Note, it is usually best to contact me at rostedt@...dmis.org (Cc'd) as
> I don't always check this email. I especially don't check it when
> traveling, and on holidays (like next week).
> 
> On Tue, 2011-12-20 at 18:26 +0900, Hiraku TOYOOKA wrote:
>> Hello, Steven,
>> I'm researching RAS features for real-time systems.
>>
>> I'm interested in the multiple ring buffer support on ftrace because of
>> following reasons.
> 
> Yep, that has been requested before.
> 
>> * To preserve particular events such as error or fault over a long time. These
>> events are useful for failure analysis. But these events could be lost when
>> other trace events are generated in large quantities in one buffer. If there is
>> only one buffer, we have to prepare one big buffer so that the particular events
>> are not overwritten by other events. It wastes memory as a result.
>>
>> * To use the same trace events for different purposes. For example, I'd like to
>> collect trace events and detect performance degradation (using sched_switch
>> event, etc.), while running flight recorder for failure analysis.
>>
>> Multiple buffer support makes these really easy. I'm sure that other users wish
>> to use it. Of course, it will introduce some complexities to ftrace code.
> 
> Not really. I've always Nack'd the making of the global_ops non-static
> for this very reason. The events may need some work, but nothing too
> hard.
> 
>> So, I'd like to implement following the features on ftrace.
>>
>> * A mechanism to increase buffers on demand
>> * A mechanism to change destination buffer(s) of each trace event via debugfs
>>
>> I have heard from Masami that you have some ideas of multiple buffers. If so,
>> could you tell me the ideas? I'd like to cooperate with you to develop multiple
>> buffers.
> 
> Yeah, basically I figured we create another directory inside the
> debugfs/tracing directory. Maybe call it sub_buffers or something.
> Inside this directory we could have:
> 
> create_buffer - a file that you echo a name into to create a new buffer,
> then a directory with that name will appear in this directory.
> 
> echo foobar > debugfs/tracing/sub_buffers/create
> 
> ls debugfs/tracing/sub_buffers/foobar
> 
> buffer_size_kb current_tracer events set_ftrace_filter ...
> 
> basically the new directory foobar will be a copy of the debugfs/tracing
> directory with a few things possibly missing. Then each of these will be
> agnostic to the main tracer.
> 
> This was my idea, and I can think of a few issues that will come up, but
> nothing that would be a show-stopper.
> 
> -- Steve
> 
> 
> --
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-- 
Hiraku TOYOOKA
Linux Technology Center
Yokohama Research Laboratory
Hitachi Ltd.
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