Date: Tue, 13 Jul 1999 15:37:16 +1000 From: "Andrew Reilly" <a.reilly@lake.com.au> To: Mike Smith <mike@smith.net.au> Cc: Mike Haertel <mike@ducky.net>, Matthew Dillon <dillon@apollo.backplane.com>, Luoqi Chen <luoqi@watermarkgroup.com>, dfr@nlsystems.com, jeremyp@gsmx07.alcatel.com.au, freebsd-current@FreeBSD.ORG Subject: Re: "objtrm" problem probably found (was Re: Stuck in "objtrm") Message-ID: <19990713153716.A94421@gurney.reilly.home> In-Reply-To: <199907130209.TAA03301@dingo.cdrom.com>; from Mike Smith on Mon, Jul 12, 1999 at 07:09:58PM -0700 References: <199907121741.KAA17837@ducky.net> <199907130209.TAA03301@dingo.cdrom.com>
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On Mon, Jul 12, 1999 at 07:09:58PM -0700, Mike Smith wrote:
> > Although function calls are more expensive than inline code,
> > they aren't necessarily a lot more so, and function calls to
> > non-locked RMW operations are certainly much cheaper than
> > inline locked RMW operations.
>
> This is a fairly key statement in context, and an opinion here would
> count for a lot; are function calls likely to become more or less
> expensive in time?
Others have answered this question, but I thought I'd point out
that there is another alternative that is likely to be faster
than indirect function calls on some architectures: inline
branched code. So you still have a global variable selecting
locked/non-locked, but it's a boolean, rather than a pointer.
Your atomic macros are then { if (atomic_lock) asm("lock;foo");
else asm ("foo"); }
You might be interested in the paper:
"Efficient Dynamic Dispatch without Virtual Function Tables. The
SmallEiffel Compiler." Olivier ZENDRA, Dominique COLNET, Suzanne
COLLIN. 12th Annual ACM SIGPLAN Conference on Object-Oriented
Programming, Systems, Languages, and Applications (OOPSLA'97),
Volume 32, Issue 10 - Atlanta, GA, USA, October 1997, pages 125-141.
http://SmallEiffel.loria.fr/papers/papers.html#OOPSLA97
as a justification for that approach.
--
Andrew
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