linux-kernel - Re: [tip:perf/core] tools/perf: Add required memory barriers

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Date:	Mon, 11 Nov 2013 22:10:02 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Vince Weaver <vince@...ter.net>, hpa@...or.com, anton@...ba.org,
	mathieu.desnoyers@...ymtl.ca, linux-kernel@...r.kernel.org,
	michael@...erman.id.au, paulmck@...ux.vnet.ibm.com,
	benh@...nel.crashing.org, fweisbec@...il.com, VICTORK@...ibm.com,
	tglx@...utronix.de, oleg@...hat.com, mikey@...ling.org,
	linux-tip-commits@...r.kernel.org,
	Arnaldo Carvalho de Melo <acme@...radead.org>,
	Jiri Olsa <jolsa@...hat.com>,
	Namhyung Kim <namhyung@...nel.org>,
	David Ahern <dsahern@...il.com>
Subject: Re: [tip:perf/core] tools/perf: Add required memory barriers


* Peter Zijlstra <peterz@...radead.org> wrote:

> On Thu, Nov 07, 2013 at 09:21:22AM +0100, Ingo Molnar wrote:
> > 
> > * Peter Zijlstra <peterz@...radead.org> wrote:
> > 
> > > > Requiring the user of a kernel interface to have a deep knowledge of 
> > > > optimizing compilers, barriers, and CPU memory models is just asking 
> > > > for trouble.
> > > 
> > > It shouldn't be all that hard to put this in a (lgpl) library others can 
> > > link to -- that way you can build it once (using GCC).
> > 
> > I'd suggest to expose it via a new perf syscall, using vsyscall methods to 
> > not have to enter the kernel for the pure user-space bits. It should also 
> > have a real usecase in tools/perf/ so that it's constantly tested, with 
> > matching 'perf test' entries, etc.
> 
> Oh man, I've never poked at the entire vsyscall stuff before; let alone
> done it for ARM, ARM64, PPC64 etc..
> 
> Keeping it in userspace like we have is so much easier.

... and so much more broken in fantastic ways, right? ;-)

Thanks,

	Ingo
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