On Mon, Jan 14, 2013 at 10:55 PM, Glauber Costa <glommer@xxxxxxxxxxxxx> wrote:
> On 01/14/2013 12:34 AM, Sha Zhengju wrote:
>>> + struct kernel_cpustat *kcpustat = this_cpu_ptr(ca->cpustat);
>>> > +
>>> > kcpustat = this_cpu_ptr(ca->cpustat);
>> Is this reassignment unnecessary?
>>
>>
> No.
>
No? No!
In task_group_account_field(), the following two hunks have the
similar behavior but different codes, there must be a trial in one of
them.
Hunk #1:
+#ifdef CONFIG_CGROUP_SCHED
+ rcu_read_lock();
+ tg = container_of(task_subsys_state(p, cpu_cgroup_subsys_id),
+ struct task_group, css);
+ while (tg && (tg != &root_task_group)) {
+ struct kernel_cpustat *kcpustat =
this_cpu_ptr(tg->cpustat); **HERE**
+
+ kcpustat->cpustat[index] += tmp;
+ tg = tg->parent;
+ }
+ rcu_read_unlock();
+#endif
Hunk #2:
#ifdef CONFIG_CGROUP_CPUACCT
if (unlikely(!cpuacct_subsys.active))
return;
rcu_read_lock();
ca = task_ca(p);
while (ca && (ca != &root_cpuacct)) {
+ struct kernel_cpustat *kcpustat =
this_cpu_ptr(ca->cpustat); **HERE**
+
kcpustat = this_cpu_ptr(ca->cpustat); **HERE, which
is unnecessary**
kcpustat->cpustat[index] += tmp;
ca = parent_ca(ca);
}
rcu_read_unlock();
#endif
Also you can prove it by the following testcase.
#include <stdio.h>
int main(void)
{
int i = 0;
int array[10] = {0, 1, 2, 3, 4, 5, 6, 7, 8, 9};
int *index = &array[0];
while (i < 10) {
int *ptr = index;
printf("ptr=%d %p, index = %d\n", *ptr, ptr, *index);
index ++;
i++;
sleep(1);
}
return 0;
}
--
Thanks,
Sha
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