From mboxrd@z Thu Jan 1 00:00:00 1970 From: Russell King - ARM Linux Date: Mon, 04 Jan 2016 13:59:34 +0000 Subject: Re: [PATCH v2 17/32] arm: define __smp_xxx Message-Id: <20160104135934.GE19062@n2100.arm.linux.org.uk> List-Id: References: <1451572003-2440-1-git-send-email-mst@redhat.com> <1451572003-2440-18-git-send-email-mst@redhat.com> <20160102112438.GU8644@n2100.arm.linux.org.uk> <20160103110158-mutt-send-email-mst@redhat.com> <20160104133658.GY6344@twins.programming.kicks-ass.net> <20160104135420.GS6373@twins.programming.kicks-ass.net> In-Reply-To: <20160104135420.GS6373@twins.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Peter Zijlstra Cc: "Michael S. Tsirkin" , linux-kernel@vger.kernel.org, Arnd Bergmann , linux-arch@vger.kernel.org, Andrew Cooper , virtualization@lists.linux-foundation.org, Stefano Stabellini , Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , David Miller , linux-ia64@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-s390@vger.kernel.org, sparclinux@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-metag@vger.kernel.org, linux-mips@linux-mips.org, x86@kernel.org, user-mode-linux-devel@lists.sourceforge.net, adi-buildroot-devel@lists.sourceforge.net, linux-sh@vger.kernel.org, linux-xtensa@linux-xtensa.org, xen-devel@lists.xenproject.org, Ingo Molnar , Tony Lindgren Andre On Mon, Jan 04, 2016 at 02:54:20PM +0100, Peter Zijlstra wrote: > On Mon, Jan 04, 2016 at 02:36:58PM +0100, Peter Zijlstra wrote: > > On Sun, Jan 03, 2016 at 11:12:44AM +0200, Michael S. Tsirkin wrote: > > > On Sat, Jan 02, 2016 at 11:24:38AM +0000, Russell King - ARM Linux wrote: > > > > > > My only concern is that it gives people an additional handle onto a > > > > "new" set of barriers - just because they're prefixed with __* > > > > unfortunately doesn't stop anyone from using it (been there with > > > > other arch stuff before.) > > > > > > > > I wonder whether we should consider making the smp memory barriers > > > > inline functions, so these __smp_xxx() variants can be undef'd > > > > afterwards, thereby preventing drivers getting their hands on these > > > > new macros? > > > > > > That'd be tricky to do cleanly since asm-generic depends on > > > ifndef to add generic variants where needed. > > > > > > But it would be possible to add a checkpatch test for this. > > > > Wasn't the whole purpose of these things for 'drivers' (namely > > virtio/xen hypervisor interaction) to use these? > > Ah, I see, you add virt_*mb() stuff later on for that use case. > > So, assuming everybody does include asm-generic/barrier.h, you could > simply #undef the __smp version at the end of that, once we've generated > all the regular primitives from it, no? Not so simple - that's why I mentioned using inline functions. The new smp_* _macros_ are: +#define smp_mb() __smp_mb() which means if we simply #undef __smp_mb(), smp_mb() then points at something which is no longer available, and we'll end up with errors saying that __smp_mb() doesn't exist. My suggestion was to change: #ifndef smp_mb #define smp_mb() __smp_mb() #endif to: #ifndef smp_mb static inline void smp_mb(void) { __smp_mb(); } #endif which then means __smp_mb() and friends can be #undef'd afterwards. -- RMK's Patch system: http://www.arm.linux.org.uk/developer/patches/ FTTC broadband for 0.8mile line: currently at 9.6Mbps down 400kbps up according to speedtest.net.