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    SubjectRE: [PATCH v7 0/4] arch: Add lightweight memory barriers for coherent memory access
    Date
    > -----Original Message-----
    > From: Alexander Duyck [mailto:alexander.duyck@gmail.com]
    > Sent: Wednesday, December 10, 2014 9:29 PM
    > To: Alexander Duyck; linux-arch@vger.kernel.org; netdev@vger.kernel.org;
    > linux-kernel@vger.kernel.org; arnd@arndb.de; davem@davemloft.net
    > Cc: mathieu.desnoyers@polymtl.ca; peterz@infradead.org;
    > benh@kernel.crashing.org; heiko.carstens@de.ibm.com; mingo@kernel.org;
    > mikey@neuling.org; linux@arm.linux.org.uk; Skidmore, Donald C; Vick,
    > Matthew; geert@linux-m68k.org; Kirsher, Jeffrey T; romieu@fr.zoreil.com;
    > paulmck@linux.vnet.ibm.com; nic_swsd@realtek.com;
    > will.deacon@arm.com; michael@ellerman.id.au; Luck, Tony; torvalds@linux-
    > foundation.org; oleg@redhat.com; schwidefsky@de.ibm.com;
    > fweisbec@gmail.com
    > Subject: Re: [PATCH v7 0/4] arch: Add lightweight memory barriers for
    > coherent memory access
    >
    > On 11/25/2014 12:35 PM, Alexander Duyck wrote:
    > > 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 v7 for:
    > > v4-6: 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:
    > > v7:
    > > - Dropped test/debug patch that was accidentally slipped in
    > > v6:
    > > - Replaced "memory based device I/O" with "consistent memory" in
    > > docs
    > > - Added reference to DMA-API.txt to explain consistent memory
    > > 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 | 42 +++++++++++++++
    > > 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, 258 insertions(+), 179 deletions(-)
    > >
    > > --
    >
    > It occurs to me that I never got a sign off from any of the maintainers on
    > getting this pulled in.
    >
    > Since the merge window is open I was wondering which tree I should make
    > sure these patches apply to and who will be the one to pull them in?
    > Since I was modifying network drivers should I resubmit them for netdev, or
    > should I submit them for asm-generic or some other tree?
    >
    > - Alex

    For at least ixgbe, it looks good to me.

    Acked-by: Don Skidmore <donald.c.skidmore@intel.com>

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