diff options
| author | Will Deacon <will.deacon@arm.com> | 2010-05-24 12:11:43 -0700 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@suse.de> | 2010-08-02 10:29:45 -0700 |
| commit | be25710fff49935664a4cecd7ac52a1d804049e1 (patch) | |
| tree | d304289b76ba56326109863caa925d99df5ed8b7 /kernel | |
| parent | 06c8d8c33e4a0e2181c42dfa3a8eb9702f9848ac (diff) | |
sched: Prevent compiler from optimising the sched_avg_update() loop
commit 0d98bb2656e9bd2dfda2d089db1fe1dbdab41504 upstream.
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>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
Diffstat (limited to 'kernel')
| -rw-r--r-- | kernel/sched.c | 6 |
1 files changed, 6 insertions, 0 deletions
diff --git a/kernel/sched.c b/kernel/sched.c index 3c2a54f70ff..37b88b0cf10 100644 --- a/kernel/sched.c +++ b/kernel/sched.c @@ -1251,6 +1251,12 @@ static void sched_avg_update(struct rq *rq) s64 period = sched_avg_period(); while ((s64)(rq->clock - rq->age_stamp) > period) { + /* + * Inline assembly required to prevent the compiler + * optimising this loop into a divmod call. + * See __iter_div_u64_rem() for another example of this. + */ + asm("" : "+rm" (rq->age_stamp)); rq->age_stamp += period; rq->rt_avg /= 2; } |