linux-kernel - Re: [Patch 11/12] ftrace plugin for kernel symbol tracing using HW Breakpoint interfaces

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Date:	Fri, 24 Apr 2009 22:57:44 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	"K.Prasad" <prasad@...ux.vnet.ibm.com>
Cc:	Alan Stern <stern@...land.harvard.edu>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ingo Molnar <mingo@...e.hu>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Benjamin Herrenschmidt <benh@....ibm.com>,
	maneesh@...ux.vnet.ibm.com, Roland McGrath <roland@...hat.com>,
	Steven Rostedt <srostedt@...hat.com>
Subject: Re: [Patch 11/12] ftrace plugin for kernel symbol tracing using HW
	Breakpoint interfaces - v3

On Fri, Apr 24, 2009 at 02:43:47PM +0530, K.Prasad wrote:
> On Fri, Apr 24, 2009 at 09:21:42AM +0200, Frederic Weisbecker wrote:
> > On Fri, Apr 24, 2009 at 11:48:50AM +0530, K.Prasad wrote:
> > > This patch adds an ftrace plugin to detect and profile memory access over kernel
> > > variables. It uses HW Breakpoint interfaces to 'watch memory addresses.
> > 
> > 
> > Just a small concern, but it would be nice if you could include the history
> > of this patch in the changelogs.
> > 
> > 
> >
> 
> Hi Frederic,
> 	Thanks for looking into the patch. I will provide the history of
> changes here. The ULONG_MAX definition from linux/kernel.h is now used
> and the permission for the 'ksym_trace_filter' file is now set to 644
> (similar to other ftrace plugin filters).
> 
> Changelog
> ---------
> (since the first post of this patch here: http://lkml.org/lkml/2009/3/4/418)
> 
> - Addition of a startup selftest to test basic sanity of HW Breakpoint
>   infrastructure.
> - Implementation of a ftrace's stats facility over ksym_tracer to
>   provide aggregate 'hit' counter values.
> - Conversion of all locking primitives into spinlocks (ksym_tracer_lock)
>   from previous mutex implementation (since stats collection happens inside
>   the context of the breakpoint exception and we cannot sleep).
> - A few changes in ksym_trace_filter_write() and
>   process_new_ksym_entry() to eliminate passing of unnecessary values.
> - Fixed a few potential memory leak scenarios (missing kfree()
>   operations in return path) along with other minor issues pointed out in LKML.
> - Minor code changes such as unconditional definition of 'struct
>   trace_ksym' - irrespective of CONFIG_KSYM_TRACER.



Thanks! Such history is very useful to understand a patch. They
can explain some logic reasoning of a patch, especially between
versions.


 
> ftrace plugin for kernel symbol tracing using HW Breakpoint interfaces - v3
> 
> This patch adds an ftrace plugin to detect and profile memory access over kernel
> variables. It uses HW Breakpoint interfaces to 'watch memory addresses.
> 
> Signed-off-by: K.Prasad <prasad@...ux.vnet.ibm.com>


It looks good.
Thanks!

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