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[v4,1/3] eal: adjust barriers for IO on Armv8-a

Message ID 20200706234333.26310-1-honnappa.nagarahalli@arm.com (mailing list archive)
State Accepted, archived
Delegated to: David Marchand
Headers show
Series [v4,1/3] eal: adjust barriers for IO on Armv8-a | expand


Context Check Description
ci/Intel-compilation fail apply issues
ci/iol-mellanox-Performance success Performance Testing PASS
ci/iol-testing success Testing PASS
ci/iol-intel-Performance success Performance Testing PASS
ci/iol-broadcom-Performance success Performance Testing PASS
ci/checkpatch warning coding style issues

Commit Message

Honnappa Nagarahalli July 6, 2020, 11:43 p.m. UTC
Change the barrier APIs for IO to reflect that Armv8-a is other-multi-copy
atomicity memory model.

Armv8-a memory model has been strengthened to require
other-multi-copy atomicity. This property requires memory accesses
from an observer to become visible to all other observers
simultaneously [3]. This means

a) A write arriving at an endpoint shared between multiple CPUs is
   visible to all CPUs
b) A write that is visible to all CPUs is also visible to all other
   observers in the shareability domain

This allows for using cheaper DMB instructions in the place of DSB
for devices that are visible to all CPUs (i.e. devices that DPDK
caters to).

Please refer to [1], [2] and [3] for more information.

[1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=22ec71615d824f4f11d38d0e55a88d8956b7e45f
[2] https://www.youtube.com/watch?v=i6DayghhA8Q
[3] https://www.cl.cam.ac.uk/~pes20/armv8-mca/

Signed-off-by: Honnappa Nagarahalli <honnappa.nagarahalli@arm.com>
Acked-by: Jerin Jacob <jerinj@marvell.com>
Tested-by: Ruifeng Wang <ruifeng.wang@arm.com>
 lib/librte_eal/arm/include/rte_atomic_64.h | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)
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diff --git a/lib/librte_eal/arm/include/rte_atomic_64.h b/lib/librte_eal/arm/include/rte_atomic_64.h
index 7b7099cdc..e42f69edc 100644
--- a/lib/librte_eal/arm/include/rte_atomic_64.h
+++ b/lib/librte_eal/arm/include/rte_atomic_64.h
@@ -1,6 +1,6 @@ 
 /* SPDX-License-Identifier: BSD-3-Clause
  * Copyright(c) 2015 Cavium, Inc
- * Copyright(c) 2019 Arm Limited
+ * Copyright(c) 2020 Arm Limited
 #ifndef _RTE_ATOMIC_ARM64_H_
@@ -19,11 +19,11 @@  extern "C" {
 #include <rte_compat.h>
 #include <rte_debug.h>
-#define rte_mb() asm volatile("dsb sy" : : : "memory")
+#define rte_mb() asm volatile("dmb osh" : : : "memory")
-#define rte_wmb() asm volatile("dsb st" : : : "memory")
+#define rte_wmb() asm volatile("dmb oshst" : : : "memory")
-#define rte_rmb() asm volatile("dsb ld" : : : "memory")
+#define rte_rmb() asm volatile("dmb oshld" : : : "memory")
 #define rte_smp_mb() asm volatile("dmb ish" : : : "memory")
@@ -37,9 +37,9 @@  extern "C" {
 #define rte_io_rmb() rte_rmb()
-#define rte_cio_wmb() asm volatile("dmb oshst" : : : "memory")
+#define rte_cio_wmb() rte_wmb()
-#define rte_cio_rmb() asm volatile("dmb oshld" : : : "memory")
+#define rte_cio_rmb() rte_rmb()
 /*------------------------ 128 bit atomic operations -------------------------*/