Changes since v1: - replaced my asm-generic patch with an equivalent patch already in tip - add wrappers with virt_ prefix for better code annotation, as suggested by David Miller - dropped XXX in patch names as this makes vger choke, Cc all relevant mailing lists on all patches (not personal email, as the list becomes too long then)
I parked this in vhost tree for now, but the inclusion of patch 1 from tip creates a merge conflict (even though it's easy to resolve). Would tip maintainers prefer merging it through tip tree instead (including the virtio patches)? Or should I just merge it all through my tree, including the duplicate patch, and assume conflict will be resolved? If the second, acks will be appreciated. Thanks! This is really trying to cleanup some virt code, as suggested by Peter, who said > You could of course go fix that instead of mutilating things into > sort-of functional state. This work is needed for virtio, so it's probably easiest to merge it through my tree - is this fine by everyone? Arnd, if you agree, could you ack this please? Note to arch maintainers: please don't cherry-pick patches out of this patchset as it's been structured in this order to avoid breaking bisect. Please send acks instead! Sometimes, virtualization is weird. For example, virtio does this (conceptually): #ifdef CONFIG_SMP smp_mb(); #else mb(); #endif Similarly, Xen calls mb() when it's not doing any MMIO at all. Of course it's wrong in the sense that it's suboptimal. What we would really like is to have, on UP, exactly the same barrier as on SMP. This is because a UP guest can run on an SMP host. But Linux doesn't provide this ability: if CONFIG_SMP is not defined is optimizes most barriers out to a compiler barrier. Consider for example x86: what we want is xchg (NOT mfence - there's no real IO going on here - just switching out of the VM - more like a function call really) but if built without CONFIG_SMP smp_store_mb does not include this. Virt in general is probably the only use-case, because this really is an artifact of interfacing with an SMP host while running an UP kernel, but since we have (at least) two users, it seems to make sense to put these APIs in a central place. In fact, smp_ barriers are stubs on !SMP, so they can be defined as follows: arch/XXX/include/asm/barrier.h: #define __smp_mb() DOSOMETHING include/asm-generic/barrier.h: #ifdef CONFIG_SMP #define smp_mb() __smp_mb() #else #define smp_mb() barrier() #endif This has the benefit of cleaning out a bunch of duplicated ifdefs on a bunch of architectures - this patchset brings about a net reduction in LOC, even with new barriers and extra documentation :) Then virt can use __smp_XXX when talking to an SMP host. To make those users explicit, this patchset adds virt_xxx wrappers for them. Touching all archs is a tad tedious, but its fairly straight forward. The rest of the patchset is structured as follows: -. Patch 1 fixes a bug in asm-generic. It is already in tip, included here for completeness. -. Patches 2-12 make sure barrier.h on all remaining architectures includes asm-generic/barrier.h: after the change in Patch 1, code there matches asm-generic/barrier.h almost verbatim. Minor code tweaks were required in a couple of places. Macros duplicated from asm-generic/barrier.h are dropped in the process. After all that preparatory work, we are getting to the actual change. -. Patches 13 adds generic smp_XXX wrappers in asm-generic these select __smp_XXX or barrier() depending on CONFIG_SMP -. Patches 14-27 change all architectures to define __smp_XXX macros; the generic code in asm-generic/barrier.h then defines smp_XXX macros I compiled the affected arches before and after the changes, dumped the .text section (using objdump -O binary) and made sure that the object code is exactly identical before and after the change. I couldn't fully build sh,tile,xtensa but I did this test kernel/rcu/tree.o kernel/sched/wait.o and kernel/futex.o and tested these instead. Unfortunately, I don't have a metag cross-build toolset ready. Hoping for some acks on this architecture. Finally, the following patches put the __smp_xxx APIs to work for virt: -. Patch 28 adds virt_ wrappers for __smp_, and documents them. After all this work, this requires very few lines of code in the generic header. -. Patches 29,30,33,34 convert virtio xen drivers to use the virt_xxx APIs xen patches are untested virtio ones have been tested on x86 -. Patches 31-32 teach virtio to use virt_store_mb sh architecture was missing a 2-byte smp_store_mb, the fix is trivial although my code is not optimal: if anyone cares, pls send me a patch to apply on top. I didn't build this architecture, but intel's 0-day infrastructure builds it. tested on x86 Davidlohr Bueso (1): lcoking/barriers, arch: Use smp barriers in smp_store_release() Michael S. Tsirkin (33): asm-generic: guard smp_store_release/load_acquire ia64: rename nop->iosapic_nop ia64: reuse asm-generic/barrier.h powerpc: reuse asm-generic/barrier.h s390: reuse asm-generic/barrier.h sparc: reuse asm-generic/barrier.h arm: reuse asm-generic/barrier.h arm64: reuse asm-generic/barrier.h metag: reuse asm-generic/barrier.h mips: reuse asm-generic/barrier.h x86/um: reuse asm-generic/barrier.h x86: reuse asm-generic/barrier.h asm-generic: add __smp_xxx wrappers powerpc: define __smp_xxx arm64: define __smp_xxx arm: define __smp_xxx blackfin: define __smp_xxx ia64: define __smp_xxx metag: define __smp_xxx mips: define __smp_xxx s390: define __smp_xxx sh: define __smp_xxx, fix smp_store_mb for !SMP sparc: define __smp_xxx tile: define __smp_xxx xtensa: define __smp_xxx x86: define __smp_xxx asm-generic: implement virt_xxx memory barriers Revert "virtio_ring: Update weak barriers to use dma_wmb/rmb" virtio_ring: update weak barriers to use __smp_XXX sh: support a 2-byte smp_store_mb virtio_ring: use virt_store_mb xenbus: use virt_xxx barriers xen/io: use virt_xxx barriers arch/arm/include/asm/barrier.h | 35 ++----------- arch/arm64/include/asm/barrier.h | 19 +++---- arch/blackfin/include/asm/barrier.h | 4 +- arch/ia64/include/asm/barrier.h | 24 +++------ arch/metag/include/asm/barrier.h | 55 ++++++------------- arch/mips/include/asm/barrier.h | 51 ++++++------------ arch/powerpc/include/asm/barrier.h | 33 ++++-------- arch/s390/include/asm/barrier.h | 25 ++++----- arch/sh/include/asm/barrier.h | 11 +++- arch/sparc/include/asm/barrier_32.h | 1 - arch/sparc/include/asm/barrier_64.h | 29 +++------- arch/sparc/include/asm/processor.h | 3 -- arch/tile/include/asm/barrier.h | 9 ++-- arch/x86/include/asm/barrier.h | 36 +++++-------- arch/x86/um/asm/barrier.h | 9 +--- arch/xtensa/include/asm/barrier.h | 4 +- include/asm-generic/barrier.h | 102 ++++++++++++++++++++++++++++++++---- include/linux/virtio_ring.h | 22 +++++--- include/xen/interface/io/ring.h | 16 +++--- arch/ia64/kernel/iosapic.c | 6 +-- drivers/virtio/virtio_ring.c | 15 +++--- drivers/xen/xenbus/xenbus_comms.c | 8 +-- Documentation/memory-barriers.txt | 28 ++++++++-- 23 files changed, 266 insertions(+), 279 deletions(-) -- MST _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@lists.ozlabs.org https://lists.ozlabs.org/listinfo/linuxppc-dev