Date: Wed, 2 Dec 2009 11:28:01 +0530
From: Sripathi Kodi <sripathik@in.ibm.com>
To: Ingo Molnar <mingo@elte.hu>
Cc: Darren Hart <dvhltc@us.ibm.com>, Peter Zijlstra <peterz@infradead.org>,
       Fr??d??ric Weisbecker <fweisbec@gmail.com>,
       Thomas Gleixner <tglx@linutronix.de>, linux-kernel@vger.kernel.org
Subject: Re: [RFC] [PATCH 0/2] Futex fault injection
Message-ID: <20091202112801.51af65c0@sripathi>
In-Reply-To: <20091201162359.GA1079@elte.hu>
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	<20091201162359.GA1079@elte.hu>
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On Tue, 1 Dec 2009 17:23:59 +0100
Ingo Molnar <mingo@elte.hu> wrote:

> 
> * Darren Hart <dvhltc@us.ibm.com> wrote:
> 
> > I don't think the "butt-ugly" argument is enough to reject the patch. 
> 
> It is in my book - i dont ever apply ugly patches intentionally.
> 
> > It's a fairly subjective metric and I don't think the proposed 
> > solution results in "pretty" code either. In fact the super long 
> > function names and multi-line conditionals are arguably "ugly" (maybe 
> > not "butt-ugly" though). :-)
> >
> > However, the arguments are solid and I understand wanting to introduce 
> > a new feature in a particular way. Has there been any work done on 
> > perf event injection up to this point or would this be a completely 
> > new perf feature?
> 
> Yeah, it would be a brand new one.
> 

Fault injection framework currently in the kernel provides an
infrastructure to set parameters like 'probability', 'interval',
'times' as well as a task filter. I think a fault injection mechanism
using tracepoints-perf will also need to provide such a framework,
because without that the faults become too predictable. For example, if
there are 20 fault points in the kernel, we should be able to trigger
any one of them with a given probability, possibly for a particular
task alone. This infrastructure will have to be built in perf tools in
user space. Do you agree?

Thanks,
Sripathi.

> There's a couple of other usecases as well:
> 
>  - User space logging: apps want to define tracepoints and want to
>    inject events as they happen - mixed properly into the regular perf
>    events flow.
> 
>  - MCE logging: hw faults are so rare that injection is desired to make
>    sure the policy action chain is working properly.
> 
>  - Some of the other fault injection sites could be converted to
>    tracepoints + injection-conditions as well, perhaps. That would give
>    a more programmable interface and a generic event logging framework.
> 
> So it's nice and important work (and by no means trivial - that comes 
> with the territory) - in case you are interested.
> 
> Thanks,
> 
> 	Ingo
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