From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Michael S. Tsirkin" Subject: Re: [PATCH v2 22/32] s390: define __smp_xxx Date: Mon, 4 Jan 2016 22:18:58 +0200 Message-ID: <20160104221323-mutt-send-email-mst__24242.5600103617$1451938759$gmane$org@redhat.com> References: <1451572003-2440-1-git-send-email-mst@redhat.com> <1451572003-2440-23-git-send-email-mst@redhat.com> <20160104134525.GA6344@twins.programming.kicks-ass.net> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline In-Reply-To: <20160104134525.GA6344@twins.programming.kicks-ass.net> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: virtualization-bounces@lists.linux-foundation.org Errors-To: virtualization-bounces@lists.linux-foundation.org To: Peter Zijlstra Cc: linux-mips@linux-mips.org, linux-ia64@vger.kernel.org, linux-sh@vger.kernel.org, Heiko Carstens , virtualization@lists.linux-foundation.org, "H. Peter Anvin" , sparclinux@vger.kernel.org, Ingo Molnar , linux-arch@vger.kernel.org, linux-s390@vger.kernel.org, Davidlohr Bueso , Arnd Bergmann , x86@kernel.org, Christian Borntraeger , xen-devel@lists.xenproject.org, Ingo Molnar , linux-xtensa@linux-xtensa.org, user-mode-linux-devel@lists.sourceforge.net, Stefano Stabellini , Andrey Konovalov , adi-buildroot-devel@lists.sourceforge.net, Thomas Gleixner , linux-metag@vger.kernel.org, linux-arm-kernel@lists.infradead.org, Andrew Cooper linux- List-Id: virtualization@lists.linuxfoundation.org On Mon, Jan 04, 2016 at 02:45:25PM +0100, Peter Zijlstra wrote: > On Thu, Dec 31, 2015 at 09:08:38PM +0200, Michael S. Tsirkin wrote: > > This defines __smp_xxx barriers for s390, > > for use by virtualization. > > > > Some smp_xxx barriers are removed as they are > > defined correctly by asm-generic/barriers.h > > > > Note: smp_mb, smp_rmb and smp_wmb are defined as full barriers > > unconditionally on this architecture. > > > > Signed-off-by: Michael S. Tsirkin > > Acked-by: Arnd Bergmann > > --- > > arch/s390/include/asm/barrier.h | 15 +++++++++------ > > 1 file changed, 9 insertions(+), 6 deletions(-) > > > > diff --git a/arch/s390/include/asm/barrier.h b/arch/s390/include/asm/barrier.h > > index c358c31..fbd25b2 100644 > > --- a/arch/s390/include/asm/barrier.h > > +++ b/arch/s390/include/asm/barrier.h > > @@ -26,18 +26,21 @@ > > #define wmb() barrier() > > #define dma_rmb() mb() > > #define dma_wmb() mb() > > -#define smp_mb() mb() > > -#define smp_rmb() rmb() > > -#define smp_wmb() wmb() > > - > > -#define smp_store_release(p, v) \ > > +#define __smp_mb() mb() > > +#define __smp_rmb() rmb() > > +#define __smp_wmb() wmb() > > +#define smp_mb() __smp_mb() > > +#define smp_rmb() __smp_rmb() > > +#define smp_wmb() __smp_wmb() > > Why define the smp_*mb() primitives here? Would not the inclusion of > asm-generic/barrier.h do this? No because the generic one is a nop on !SMP, this one isn't. Pls note this patch is just reordering code without making functional changes. And at the moment, on s390 smp_xxx barriers are always non empty. Some of this could be sub-optimal, but since on s390 Linux always runs on a hypervisor, I am not sure it's safe to use the generic version - in other words, it just might be that for s390 smp_ and virt_ barriers must be equivalent. If in fact this turns out to be wrong, I can pick up a patch to change this, but I'd rather make this a patch on top so that my patches are testable just by compiling and comparing the binary. -- MST