linux-kernel - Re: [PATCH 0/2] A kernel tracing interface

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Date:	Tue, 18 Sep 2007 09:53:03 -0700
From:	Vara Prasad <prasadav@...ibm.com>
To:	David Wilder <dwilder@...ibm.com>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org,
	SystemTAP <systemtap@...rces.redhat.com>,
	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
Subject: Re: [PATCH 0/2] A kernel tracing interface

David Wilder wrote:

> Andrew Morton wrote:
>
>> On Thu, 13 Sep 2007 16:43:09 -0700
>> David Wilder <dwilder@...ibm.com> wrote:
>>
>>> These patches provide a kernel tracing interface called "trace".
>>>
>>> The motivation for "trace" is to:
>>> - Provide a simple set of tracing primitives that will utilize the 
>>> high-
>>>   performance and low-overhead of relayfs for passing traces data from
>>>   kernel to user space.
>>> - Provide a common user interface for managing kernel traces.
>>> - Allow for binary as well as ascii trace data.
>>> - Incorporate features from the systemtap runtime that are
>>>   useful to others.
>>>
>>> History- Versions of this code have been submitted for review under
>>> a couple of different names.  The original submission was called UTT,
>>> it was later re-submitted as GTSC.   Christoph Hellwig commented "The
>>> code looks fine ...but the name is just dumb".  Following Christoph's
>>> advice, I changed the name to simply "Trace".
>>>
>>> This patch addresses review comments made by Christoph Hellwig and 
>>> Mathieu
>>> Desnoyers.  Changes include the addition of a mutex and synchronization
>>> protecting trace state changes (using RCU) and the reduction of the
>>> number of exports.
>>>
>>> Patches are against 2.6.23-rc4-mm1
>>>
>>> Required patches:
>>> 1/2 Trace code and documentation
>>> 2/2 Relay reset consumed  (required for trace's "rewind" feature")
>>>
>>> Signed-off-by: David Wilder <dwilder@...ibm.com>
>>
>>
>> Well the code looks neat and easy enough to merge.
>>
>> What exactly is the relationship between this and systemtap and 
>> kprobes and
>> all the other tracing things which people are doing?
>>
>>
> The key to the relationship is relay.  Systemtap, kprobes, blktrace 
> ,(and others) need the fast user-kernel data hose that relay provides. 
> Trace is a means to simplify and standardize the use of relay. 
> Systemtap adopted this code some time ago in its own runtime.  Moving 
> this code into the kernel will allow other tracers to take advantage 
> of the same trace primitives.

Andrew,

This is part of the effort by the SystemTap team to move pieces of the 
project that are generic to mainline.

bye,
Vara Prasad

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