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Message-ID: <20090305132807.GA4322@elte.hu>
Date: Thu, 5 Mar 2009 14:28:07 +0100
From: Ingo Molnar <mingo@...e.hu>
To: "K.Prasad" <prasad@...ux.vnet.ibm.com>
Cc: Frederic 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
* K.Prasad <prasad@...ux.vnet.ibm.com> wrote:
> On Thu, Mar 05, 2009 at 10:16:11AM +0100, Ingo Molnar wrote:
> >
> > * 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
>
> Thanks for the comments.
>
> Test-cases for the hardware breakpoint interfaces can be the following:
>
> - Basic sanity test to check if the API is intact
> - Perform various types of memory accesses, like read, write (I/O and
> others when implemented) on a dummy kernel variable and verify the
> trigger of the exception handler.
>
> While the above can be a part of trace_selftest_startup_ksym(),
> rigorous testing would involve:
>
> i) stressing the HW breakpoint infrastructure to confirm sane behaviour
> when interoperated with other users of a)breakpoint register b)the
> do_debug() exception. This will involve simultaneous use of kprobes,
> hardware breakpoint interface and requests from user-space (say through
> GDB).
> ii) Verifying successful HB_NUM number of register_ requests.
> iii) Verifying right priority resolution, and handling user-space
> requests.
>
> These, in my opinion, would better fit in a full-featured
> test-suite such as LTP, as opposed to startup testing in
> ftrace.
sure. It's just a quick self-test to make sure basic
functionality is ok.
> I will implement trace_selftest_startup_ksym() to contain the
> first two test-cases in the next iteration of this code.
Thanks.
Ingo
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