From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jeremy Fitzhardinge Subject: Re: [patch 12/17] Consistently wrap paravirt ops callsites to make them patchable Date: Mon, 02 Apr 2007 00:20:08 -0700 Message-ID: <4610AEA8.7010604@goop.org> References: <20070402055652.610711908@goop.org> <20070402055705.090656820@goop.org> <200704020911.50623.ak@suse.de> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-15 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <200704020911.50623.ak@suse.de> Sender: linux-kernel-owner@vger.kernel.org To: Andi Kleen Cc: Andrew Morton , virtualization@lists.osdl.org, lkml , Rusty Russell , Zachary Amsden , Anthony Liguori List-Id: virtualization@lists.linuxfoundation.org Andi Kleen wrote: > Can you please add some comments to the code explaining this a little? > Best would be perhaps a overview document in Documentation too. > Yes, OK. >> +#define PVOP_CALL0(__rettype, __op) \ >> > > The __s shouldn't be needed for the macro arguments because > there is no shared name space with the caller. > Yes. I was more concerned about "op" clashing with variables used within the macro, but that's not an issue now. >> + ({ \ >> + __rettype __ret; \ >> + if (sizeof(__rettype) > sizeof(unsigned long)) { \ >> + unsigned long long __tmp; \ >> + unsigned long __ecx; \ >> + asm volatile(paravirt_alt(PARAVIRT_CALL) \ >> > > Not having the volatile would probably generate better code, but it > seems much safer for now. > I think it has to be there, though perhaps the "memory" is sufficient to make sure all the calls get generated. We don't want gcc to eliminate any of these calls because it thinks they can be CSEd. > And the cc clobber is also not needed > I get conflicting advice about this. I think Linus mentioned that the gcc people would prefer it to be there explicitly, even though its currently implied. J