On Wed, 2 Jan 2019, Michael S. Tsirkin wrote: > So as explained in Documentation/memory-barriers.txt e.g. > a load followed by a store require a full memory barrier, > to avoid store being ordered before the load. > Similarly load-load requires a read memory barrier. > > Thinking about it, we can actually create a data dependency > by mixing the first loaded value into the pointer being > accessed. > > This adds an API for this and uses it in virtio. > > Written over the holiday and build tested only so far. You are using the terminology from memory-barriers.txt, referring to the new dependency you create as a data dependency. However, tools/memory-model/* uses a more precise name, calling it an address dependency. Could you change the comments in the patches to use this name instead? > This patchset is also suboptimal on e.g. x86 where e.g. smp_rmb is a nop. This should be easy to fix with an architecture-specific override. Alan Stern > Sending out for early feedback/flames. > > Michael S. Tsirkin (4): > include/linux/compiler*.h: fix OPTIMIZER_HIDE_VAR > include/linux/compiler.h: allow memory operands > barriers: convert a control to a data dependency > virtio: use dependent_ptr_mb > > Documentation/memory-barriers.txt | 20 ++++++++++++++++++++ > arch/alpha/include/asm/barrier.h | 1 + > drivers/virtio/virtio_ring.c | 6 ++++-- > include/asm-generic/barrier.h | 18 ++++++++++++++++++ > include/linux/compiler-clang.h | 5 ++--- > include/linux/compiler-gcc.h | 4 ---- > include/linux/compiler-intel.h | 4 +--- > include/linux/compiler.h | 8 +++++++- > 8 files changed, 53 insertions(+), 13 deletions(-)
