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Message-ID: <20090309213644.GA8103@in.ibm.com>
Date: Tue, 10 Mar 2009 03:06:44 +0530
From: "K.Prasad" <prasad@...ux.vnet.ibm.com>
To: Ingo Molnar <mingo@...e.hu>
Cc: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
Frédéric Weisbecker <fweisbec@...il.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 - v2
On Sun, Mar 08, 2009 at 11:09:29AM +0100, Ingo Molnar wrote:
>
> * KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com> wrote:
>
> > Hi
> >
> > > 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>
> > > ---
> > > kernel/trace/Kconfig | 6
> > > kernel/trace/Makefile | 1
> > > kernel/trace/trace.h | 16 +
> > > kernel/trace/trace_ksym.c | 448 ++++++++++++++++++++++++++++++++++++++++++
> > > kernel/trace/trace_selftest.c | 36 +++
> > > 5 files changed, 507 insertions(+)
> >
> > Could you please update Documentation/ftrace.txt?
> > I guess many user interesting this patch. :)
>
> Yeah, it has become a really nice feature this way. As i told it
> to K.Prasad before: we need this tracer because the data tracer
> will likely become the most common usecase of this facility. We
> will get the hw breakpoints facility tested and used.
>
> And in fact we can go one step further: it would also be nice to
> wire it up with the ftrace histogram code: so that we can get
> usage histograms of kernel symbol read/write activities without
> the overhead of tracing. (The branch tracer already has this.)
>
> Especially frequently used variables generate a _lot_ of events.
>
> Ingo
I am looking at the histogram infrastructure, its implementation in
branch tracer for getting the same in ksym tracer. Meanwhile I'm thinking
if the patchset can be included in -tip tree for some good amount of
testing and feedback from the community before they make their way into
mainline (2.6.30?).
I will be glad if you can pick the patches to be a part of -tip tree.
Thanks,
K.Prasad
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