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Date: Tue, 21 Jun 2016 10:24:53 -0700 From: "H. Peter Anvin" <hpa@...or.com> To: David Howells <dhowells@...hat.com> Cc: Peter Zijlstra <peterz@...radead.org>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, linux-arch <linux-arch@...r.kernel.org>, Linus Torvalds <torvalds@...ux-foundation.org>, Ingo Molnar <mingo@...nel.org>, Thomas Gleixner <tglx@...utronix.de> Subject: Re: cmpxchg and x86 flags output On 06/21/16 02:06, David Howells wrote: > > However, there's probably not a great deal of difference to be had if the > inline asm codes the appropriate instruction in each case for something like > x86*. The emitted code ought to look the same. The second biggest win for > the intriniscs, I think, is the ability to ask the CMPXCHG instruction whether > it actually did anything rather than comparing the result. I added two > variants, one that only returned the yes/no and one that passed back the value > as well as the yes/no. > Right, and we want that either way. The API change that you are proposing is definitely what we want; the specifics of the x86 implementation is sort of orthogonal. -hpa
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