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

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Date:	Thu, 5 Mar 2009 10:16:11 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	prasad@...ux.vnet.ibm.com,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Alan Stern <stern@...land.harvard.edu>,
	Roland McGrath <roland@...hat.com>
Subject: Re: [patch 11/11] ftrace plugin for kernel symbol tracing using HW
	Breakpoint interfaces


* Frederic Weisbecker <fweisbec@...il.com> wrote:

> On Thu, Mar 05, 2009 at 10:13:33AM +0530, prasad@...ux.vnet.ibm.com 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.
> > 
> > Signed-off-by: K.Prasad <prasad@...ux.vnet.ibm.com> 
> > ---
> 
> 
> Hi,
> 
> Nice feature. And moreover the standardized hardware 
> breakpoints could be helpful for tracing.

yeah. The feature is much more alive now.

> Just some comments below.

One other thing:

+#ifdef CONFIG_FTRACE_SELFTEST
+int trace_selftest_startup_ksym(struct tracer *trace, struct trace_array *tr)
+{
+       /* TODO: Will be implemented later */
+       return 0;
+}
+#endif /* CONFIG_FTRACE_SELFTEST */

This needs to be implemented before i can pick the code up into 
tip:tracing, as otherwise we will not notice it fast enough if 
some of this stuff breaks.

Basically the ftrace plugin will be the main usage vector of 
this facility, so the self-test is a must-have.

Looks very nice otherwise.

	Ingo
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