linux-kernel - Re: RFC: A reduced Linux network stack for small systems

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Message-ID: <20140509073909.GE4965@xo-6d-61-c0.localdomain>
Date:	Fri, 9 May 2014 09:39:09 +0200
From:	Pavel Machek <pavel@....cz>
To:	Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc:	Tom Zanussi <tom.zanussi@...ux.intel.com>,
	Richard Weinberger <richard.weinberger@...il.com>,
	Andi Kleen <andi@...stfloor.org>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: RFC: A reduced Linux network stack for small systems

> >> that is likely working only for the given very limited set of applications.
> >> Kernel function profiling can potentially achieve the same thing.
> >> Profile the kernel with the set of apps and then prune all cold
> >> functions out of kernel.
> >
> > Right, and are Profile-Guided-Optimization results now reproduceable?
> > Better change it to Trace-Guided-Optimization.  But yeah, for a
> 
> not quite. I'm saying: no extra optimizations, no GCC changes.
> Compile kernel as-is. Most functions have a stub for mcount() already.
> Use it to track whether kernel function was called or not.
> Collect this data in userspace (as perf already does), add few
> more functions that had 'notrace' attribute on them, and feed this into
> special linker that unpacks existing vmlinux, throws away cold functions,
> relocates the rest and here you have tiny vmlinux without recompilation.

It sounds like unstripped kernel will not even fit on the target machine.
If it+application would fit there, you'd have no reason to strip it down...

									Pavel

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