linux-kernel - Re: [RFC patch 08/18] cnt32_to_63 should use smp

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Date:	Fri, 07 Nov 2008 16:21:55 +0000
From:	David Howells <dhowells@...hat.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	dhowells@...hat.com, Nicolas Pitre <nico@....org>,
	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	linux-kernel@...r.kernel.org, Ralf Baechle <ralf@...ux-mips.org>,
	benh@...nel.crashing.org, paulus@...ba.org,
	David Miller <davem@...emloft.net>,
	Ingo Molnar <mingo@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Steven Rostedt <rostedt@...dmis.org>,
	linux-arch@...r.kernel.org
Subject: Re: [RFC patch 08/18] cnt32_to_63 should use smp_rmb()

Andrew Morton <akpm@...ux-foundation.org> wrote:

> If gcc did that then it would need to generate static instances of
> inlined functions within individual compilation units.  It would be a
> disaster for the kernel.  For a start, functions which are "inlined" in kernel
> modules wouldn't be able to access their static storage and modprobing
> them would fail.

Do you expect a static inline function that lives in a header file and that
has a static variable in it to share that static variable over all instances
of that function in a program?  Or do you expect the static variable to be
limited at the file level?  Or just at the invocation level?

> Does mn10300's get_cycles() really count backwards?

Yes, because the value is generated by a pair of cascaded 16-bit hardware
down-counters.

> The first two callsites I looked at (crypto/tcrypt.c and fs/ext4/mballoc.c)
> assume that it is an upcounter.

Hmmm...  I didn't occur to me that get_cycles() was available for use outside
of arch code.  Possibly it wasn't so used when I first came up with the code.

I should probably make it count the other way.

David
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