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Re: Re: [PATCH -tip v9 25/26] kprobes: Introduce kprobe cache to reduce cache misshits
- From: Ingo Molnar <mingo at kernel dot org>
- To: Masami Hiramatsu <masami dot hiramatsu dot pt at hitachi dot com>
- Cc: linux-kernel at vger dot kernel dot org, Andi Kleen <andi at firstfloor dot org>, Ananth N Mavinakayanahalli <ananth at in dot ibm dot com>, Sandeepa Prabhu <sandeepa dot prabhu at linaro dot org>, Frederic Weisbecker <fweisbec at gmail dot com>, x86 at kernel dot org, Steven Rostedt <rostedt at goodmis dot org>, fche at redhat dot com, mingo at redhat dot com, systemtap at sourceware dot org, "H. Peter Anvin" <hpa at zytor dot com>, Thomas Gleixner <tglx at linutronix dot de>
- Date: Sat, 26 Apr 2014 09:12:14 +0200
- Subject: Re: Re: [PATCH -tip v9 25/26] kprobes: Introduce kprobe cache to reduce cache misshits
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* Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com> wrote:
> (2014/04/25 17:20), Ingo Molnar wrote:
> >
> > * Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com> wrote:
> >
> >>> So I don't think this should be a Kconfig entry, just enable it
> >>> unconditionally. That will further simplify the code.
> >>
> >> Hmm, it consumes some amount of memory (36KB/core) just for the
> >> case of several thousand of kprobes. On enterprise servers and
> >> desktop it's OK, no problem. But I think, some embedded systems
> >> with small resources will not want that. [...]
> >
> > They'll just disable kprobes in general.
>
> No, I'd like to provide kprobes (and dynamic events) to them
> (including me) for debugging and dynamic monitoring, instead of
> modifying code for adding events on their kernel. To solve some
> specific issues, specific events (not generic events) are required.
> Making local patches to add such events is an option, but it
> increases maintenance cost for rebasing. It is better to pay cost to
> maintain this kconfig on upstream as the maintainer for me instead
> of paying such ugly local cost. :(
>
> Anyway, this option is not easy for beginners, I think it should be
> defined with "if EXPERT" option and make it enabled by default.
>
> > Really, at this point complexity is our main concern.
>
> Agreed about complexity issue. However, even if we remove the
> Kconfig, we can just save 6 lines of the code, and one #ifdef block.
> Can that really solve the complexity problem?
It's more about the mental picture about how kprobes works. The fewer
binary state flags, the better.
Thanks,
Ingo