This is a micro optimization for the hot path.

- We don't need to check if @CA is NULL in parent_ca().
- We don't need to check if @CA is NULL in the beginning of the for loop.
Signed-off-by: NLi Zefan <lizefan@huawei.com>
Acked-by: NPeter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/515536A9.5000700@huawei.comSigned-off-by: NIngo Molnar <mingo@kernel.org>

So we can remove open-coded cpuacct code in cputime.c.
Signed-off-by: NLi Zefan <lizefan@huawei.com>
Acked-by: NPeter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/51553692.9060008@huawei.comSigned-off-by: NIngo Molnar <mingo@kernel.org>

So we don't open-coded initialization of cpuacct in core.c.
Signed-off-by: NLi Zefan <lizefan@huawei.com>
Acked-by: NPeter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/51553687.1060906@huawei.comSigned-off-by: NIngo Molnar <mingo@kernel.org>

Add cpuacct.h and let sched.h include it.
Signed-off-by: NLi Zefan <lizefan@huawei.com>
Acked-by: NPeter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/5155367B.2060506@huawei.comSigned-off-by: NIngo Molnar <mingo@kernel.org>