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SubjectRe: [PATCH v2 3/4] sched/deadline: add the "set_flag" argument to cpudl_find()
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On 20 November 2014 00:24, Steven Rostedt <rostedt@goodmis.org> wrote:
> On Wed, 19 Nov 2014 23:46:21 +0800
> "pang.xunlei" <pang.xunlei@linaro.org> wrote:
>
>> The call site of cpudl_find() in check_preempt_equal_dl() doesn't
>> use later_mask, so add this extra argument to distinquish the case.
>>
>> Signed-off-by: pang.xunlei <pang.xunlei@linaro.org>
>> ---
>> kernel/sched/cpudeadline.c | 6 ++++--
>> kernel/sched/cpudeadline.h | 2 +-
>> kernel/sched/deadline.c | 6 +++---
>> 3 files changed, 8 insertions(+), 6 deletions(-)
>>
>> diff --git a/kernel/sched/cpudeadline.c b/kernel/sched/cpudeadline.c
>> index c01b3aa..3047846 100644
>> --- a/kernel/sched/cpudeadline.c
>> +++ b/kernel/sched/cpudeadline.c
>> @@ -98,11 +98,12 @@ static inline int cpudl_maximum(struct cpudl *cp)
>> * @cp: the cpudl max-heap context
>> * @p: the task
>> * @later_mask: a mask to fill in with the selected CPUs (not NULL)
>> + * @set_flag: indicate if later_mask should be set
>> *
>> * Returns: int - best CPU (heap maximum if suitable)
>> */
>> int cpudl_find(struct cpudl *cp, struct task_struct *p,
>> - struct cpumask *later_mask)
>> + struct cpumask *later_mask, int set_flag)
>
> set_flag should be a bool type.
>
>> {
>> int best_cpu = -1;
>> const struct sched_dl_entity *dl_se = &p->dl;
>> @@ -114,7 +115,8 @@ int cpudl_find(struct cpudl *cp, struct task_struct *p,
>> } else if (cpumask_test_cpu(cpudl_maximum(cp), &p->cpus_allowed) &&
>> dl_time_before(dl_se->deadline, cp->elements[0].dl)) {
>> best_cpu = cpudl_maximum(cp);
>> - cpumask_set_cpu(best_cpu, later_mask);
>> + if (set_flag)
>> + cpumask_set_cpu(best_cpu, later_mask);
>
> I'm not sure this is worth it. cpumask_set_cpu() is rather efficient.
HI Steve,

Thanks for your commenting, I've rethinked this a bit.
We can do a little trick with its return value, then could avoid this
extra cpumask_set_cpu() without this extra set_flag:
1) define macros for the return values of cpudl_find(), like:
#define CPUDL_FIND_NONE -2 /* no available cpus */
#define CPUDL_FIND_CPUMASK -1 /* available cpus in later_mask */

then, with the return value >=0, means it returns the only one available cpu.

2) In the leg of "if", it can just return CPUDL_FIND_CPUMASK, as we
want to select the best_cpu in find_later_rq().
In the leg of "else if", just returns cpudl_maximum(cp), apparently
there is no need to set the later_mask, since we will definitely
select this cpu as the best_cpu in find_later_rq() .

int cpudl_find(struct cpudl *cp, struct task_struct *p,
struct cpumask *later_mask)
{
const struct sched_dl_entity *dl_se = &p->dl;

cpumask_and(later_mask, &p->cpus_allowed, &p->cpus_allowed);
if (cpumask_and(later_mask, later_mask, cp->free_cpus)) {
return CPUDL_FIND_CPUMASK;
} else if (cpumask_test_cpu(cpudl_maximum(cp), &p->cpus_allowed) &&
dl_time_before(dl_se->deadline, cp->elements[0].dl))
int cpu;

cpu = cpudl_maximum(cp);
WARN_ON(!cpu_present(cpu));
return cpu;
}

out:

return CPUDL_FIND_NONE;
}

Thus, in find_later_rq() we can change the call site code like:
best_cpu = cpudl_find(&task_rq(task)->rd->cpudl, task,
later_mask);
if (best_cpu == CPUDL_FIND_NONE)
return -1;
if (best_cpu != CPUDL_FIND_CPUMASK)
return best_cpu;

/* adjust the following code as that in RT find_lowest_rq(), omit here... */

What's your view about this?

Thanks,
Xunlei
>
>> }
>>
>> out:
>


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