From 88c35d6516fe8bf221803cefd19bc569dd41d56a Mon Sep 17 00:00:00 2001 From: kib Date: Thu, 30 Jul 2015 15:47:53 +0000 Subject: [PATCH] Improve comments. Submitted by: bde MFC after: 2 weeks --- sys/amd64/include/atomic.h | 8 ++++---- sys/i386/include/atomic.h | 6 +++--- 2 files changed, 7 insertions(+), 7 deletions(-) diff --git a/sys/amd64/include/atomic.h b/sys/amd64/include/atomic.h index 30f594c3f7fe..33d79b2cdfb6 100644 --- a/sys/amd64/include/atomic.h +++ b/sys/amd64/include/atomic.h @@ -272,10 +272,10 @@ atomic_testandset_long(volatile u_long *p, u_int v) * addresses, so we need a Store/Load barrier for sequentially * consistent fences in SMP kernels. We use "lock addl $0,mem" for a * Store/Load barrier, as recommended by the AMD Software Optimization - * Guide, and not mfence. In the kernel, we use a private per-cpu - * cache line as the target for the locked addition, to avoid - * introducing false data dependencies. In user space, we use a word - * in the stack's red zone (-8(%rsp)). + * Guide, and not mfence. To avoid false data dependencies, we use a + * special address for "mem". In the kernel, we use a private per-cpu + * cache line. In user space, we use a word in the stack's red zone + * (-8(%rsp)). * * For UP kernels, however, the memory of the single processor is * always consistent, so we only need to stop the compiler from diff --git a/sys/i386/include/atomic.h b/sys/i386/include/atomic.h index 15742a51d2a9..3242d76dce80 100644 --- a/sys/i386/include/atomic.h +++ b/sys/i386/include/atomic.h @@ -259,9 +259,9 @@ atomic_testandset_int(volatile u_int *p, u_int v) * consistent fences in SMP kernels. We use "lock addl $0,mem" for a * Store/Load barrier, as recommended by the AMD Software Optimization * Guide, and not mfence. In the kernel, we use a private per-cpu - * cache line as the target for the locked addition, to avoid - * introducing false data dependencies. In userspace, a word at the - * top of the stack is utilized. + * cache line for "mem", to avoid introducing false data + * dependencies. In user space, we use the word at the top of the + * stack. * * For UP kernels, however, the memory of the single processor is * always consistent, so we only need to stop the compiler from