From: pierre Kuo Date: Fri, 7 Apr 2017 06:37:36 +0000 (+0800) Subject: doc: Update control-dependencies section of memory-barriers.txt X-Git-Url: https://git.stricted.de/?a=commitdiff_plain;h=b26cfc48e3e03126c183f1f3960e6d69460bb852;p=GitHub%2Fmoto-9609%2Fandroid_kernel_motorola_exynos9610.git doc: Update control-dependencies section of memory-barriers.txt In the following example, if MAX is defined to be 1, then the compiler knows (Q % MAX) is equal to zero. The compiler can therefore throw away the "then" branch (and the "if"), retaining only the "else" branch. q = READ_ONCE(a); if (q % MAX) { WRITE_ONCE(b, 1); do_something(); } else { WRITE_ONCE(b, 2); do_something_else(); } It is therefore necessary to modify the example like this: q = READ_ONCE(a); - WRITE_ONCE(b, 1); + WRITE_ONCE(b, 2); do_something_else(); Signed-off-by: pierre Kuo Acked-by: Will Deacon Signed-off-by: Paul E. McKenney --- diff --git a/Documentation/memory-barriers.txt b/Documentation/memory-barriers.txt index d2b0a8d81258..08329cb857ed 100644 --- a/Documentation/memory-barriers.txt +++ b/Documentation/memory-barriers.txt @@ -768,7 +768,7 @@ equal to zero, in which case the compiler is within its rights to transform the above code into the following: q = READ_ONCE(a); - WRITE_ONCE(b, 1); + WRITE_ONCE(b, 2); do_something_else(); Given this transformation, the CPU is not required to respect the ordering