[PATCH v5 0/4] arch: Add lightweight memory barriers for coherent memory access

Alexander Duyck
2014-11-19T01:24:53Z

These patches introduce two new primitives for synchronizing cache coherent
memory writes and reads. These two new primitives are:

dma_rmb()
dma_wmb()

The first patch cleans up some unnecessary overhead related to the
definition of read_barrier_depends, smp_read_barrier_depends, and comments
related to the barrier.

The second patch adds the primitives for the applicable architectures and
asm-generic.

The third patch adds the barriers to r8169 which turns out to be a good
example of where the new barriers might be useful as they have full
rmb()/wmb() barriers ordering accesses to the descriptors and the DescOwn
bit.

The fourth patch adds support for coherent_rmb() to the Intel fm10k, igb,
and ixgbe drivers. Testing with the ixgbe driver has shown a processing
time reduction of at least 7ns per 64B frame on a Core i7-4930K.

This patch series is essentially the v4 for:
v4: Add lightweight memory barriers for coherent memory access
v3: Add lightweight memory barriers fast_rmb() and fast_wmb()
v2: Introduce load_acquire() and store_release()
v1: Introduce read_acquire()

The key changes in this patch series versus the earlier patches are:
v5:
- Renamed barriers dma_rmb and dma_wmb
- Undid smp_wmb changes in x86 and PowerPC
- Defined smp_rmb as __lwsync for SMP case on PowerPC
v4:
- Renamed barriers coherent_rmb and coherent_wmb
- Added smp_lwsync for use in smp_load_acquire/smp_store_release
v3:
- Moved away from acquire()/store() and instead focused on barriers
- Added cleanup of read_barrier_depends
- Added change in r8169 to fix cur_tx/DescOwn ordering
- Simplified changes to just replacing/moving barriers in r8169
- Added update to documentation with code example
v2:
- Renamed read_acquire() to be consistent with smp_load_acquire()
- Changed barrier used to be consistent with smp_load_acquire()
- Updated PowerPC code to use __lwsync based on IBM article
- Added store_release() as this is a viable use case for drivers
- Added r8169 patch which is able to fully use primitives
- Added fm10k/igb/ixgbe patch which is able to test performance

---

Alexander Duyck (4):
arch: Cleanup read_barrier_depends() and comments
arch: Add lightweight memory barriers dma_rmb() and dma_wmb()
r8169: Use dma_rmb() and dma_wmb() for DescOwn checks
fm10k/igb/ixgbe: Use dma_rmb on Rx descriptor reads

Documentation/memory-barriers.txt | 41 +++++++++++++++
arch/alpha/include/asm/barrier.h | 51 ++++++++++++++++++
arch/arm/include/asm/barrier.h | 4 +
arch/arm64/include/asm/barrier.h | 3 +
arch/blackfin/include/asm/barrier.h | 51 ++++++++++++++++++
arch/ia64/include/asm/barrier.h | 25 ++++-----
arch/metag/include/asm/barrier.h | 19 ++++---
arch/mips/include/asm/barrier.h | 61 ++--------------------
arch/powerpc/include/asm/barrier.h | 19 ++++---
arch/s390/include/asm/barrier.h | 7 ++-
arch/sparc/include/asm/barrier_64.h | 7 ++-
arch/x86/include/asm/barrier.h | 70 ++++---------------------
arch/x86/um/asm/barrier.h | 20 ++++---
drivers/net/ethernet/intel/fm10k/fm10k_main.c | 6 +-
drivers/net/ethernet/intel/igb/igb_main.c | 6 +-
drivers/net/ethernet/intel/ixgbe/ixgbe_main.c | 9 +--
drivers/net/ethernet/realtek/r8169.c | 29 ++++++++--
include/asm-generic/barrier.h | 8 +++
18 files changed, 257 insertions(+), 179 deletions(-)

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