linux-kernel - Re: blktrace ftrace plugin, was Re: Receive side performance issue with multi-10-GigE and NUMA

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Date:	Fri, 28 Aug 2009 10:03:21 +0800
From:	Li Zefan <lizf@...fujitsu.com>
To:	Ingo Molnar <mingo@...e.hu>
CC:	Jens Axboe <jens.axboe@...cle.com>,
	Christoph Hellwig <hch@...radead.org>, rostedt@...dmis.org,
	fweisbec@...il.com, acme@...hat.com, linux-kernel@...r.kernel.org
Subject: Re: blktrace ftrace plugin, was Re: Receive side performance issue
 with multi-10-GigE and NUMA

Ingo Molnar wrote:
> * Jens Axboe <jens.axboe@...cle.com> wrote:
> 
>> On Wed, Aug 26 2009, Christoph Hellwig wrote:
>>> On Wed, Aug 26, 2009 at 10:40:27PM +0200, Ingo Molnar wrote:
>>>> We are also converting non-trivial plugins to generic tracepoints. A 
>>>> recent example are the system call tracepoints, but we also 
>>>> converted blktrace and kmemtrace to generic tracepoints.
>>> On something semi-related: Any reason to keep the blktrace 
>>> ftrace plugin around?  I don't think there's much point in it.  
>>> It only got added in 2.6.29, and all the blktrace tooling just 
>>> uses the legacy ioctls.  All new uses should just use the 
>>> TRACE_EVENT output.
>> Lets kill it.
> 
> Agreed.
> 
> I think we should keep the relayfs and ioctl compatibility bits 
> though: blktrace has a mature user-space environment with many
> years of installed base.
> 
> We could even move those bits back to block/blktrace_compat.c or so 
> (after the ftrace plugin bits are removed), to make sure it's nicely 
> isolated.
> 
> What do you think?
> 

I'm all for removing the ftrace plugin. There're 2 concerns:

- dev_t info can't be recorded in some blk trace events. I think
  this will change in the future when we can map a request_queue to
  a unique device?

- Not all the output of ftrace plugin comes from tracepoints probing,
  but via blk_add_trace_msg(), which directly writes a string into
  ring buffer. I think they need to be converted to TRACE_EVENT.

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