sched: Prevent compiler from optimising the sched_avg_update() loop
authorWill Deacon <will.deacon@arm.com>
Mon, 24 May 2010 19:11:43 +0000 (12:11 -0700)
committerIngo Molnar <mingo@elte.hu>
Fri, 25 Jun 2010 14:11:50 +0000 (16:11 +0200)
commit0d98bb2656e9bd2dfda2d089db1fe1dbdab41504
tree2172bbdd7fb21640062b2a692ded3d9cebc2382c
parent3c93717cfa51316e4dbb471e7c0f9d243359d5f8
sched: Prevent compiler from optimising the sched_avg_update() loop

GCC 4.4.1 on ARM has been observed to replace the while loop in
sched_avg_update with a call to uldivmod, resulting in the
following build failure at link-time:

kernel/built-in.o: In function `sched_avg_update':
 kernel/sched.c:1261: undefined reference to `__aeabi_uldivmod'
 kernel/sched.c:1261: undefined reference to `__aeabi_uldivmod'
make: *** [.tmp_vmlinux1] Error 1

This patch introduces a fake data hazard to the loop body to
prevent the compiler optimising the loop away.

Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Russell King <rmk@arm.linux.org.uk>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: <stable@kernel.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
kernel/sched.c