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SubjectRe: [PATCH v6 0/2] Make find_later_rq() choose a closer cpu in topology
On Thu, Aug 17, 2017 at 6:25 PM, Byungchul Park <byungchul.park@lge.com> wrote:
> On Mon, Aug 07, 2017 at 12:50:32PM +0900, Byungchul Park wrote:
>> When cpudl_find() returns any among free_cpus, the cpu might not be
>> closer than others, considering sched domain. For example:
>>
>> this_cpu: 15
>> free_cpus: 0, 1,..., 14 (== later_mask)
>> best_cpu: 0
>>
>> topology:
>>
>> 0 --+
>> +--+
>> 1 --+ |
>> +-- ... --+
>> 2 --+ | |
>> +--+ |
>> 3 --+ |
>>
>> ... ...
>>
>> 12 --+ |
>> +--+ |
>> 13 --+ | |
>> +-- ... -+
>> 14 --+ |
>> +--+
>> 15 --+
>>
>> In this case, it would be best to select 14 since it's a free cpu and
>> closest to 15(this_cpu). However, currently the code select 0(best_cpu)
>> even though that's just any among free_cpus. Fix it.
>
> Could you let me know your opinions about this?

Patch looks good to me, I would also add a comment ontop of
fallback_cpu (I think Steve mentioned similar thing at [1])

/*
* fallback is the closest CPU in the closest SD incase
* all domains are PREFER_SIBLING
*/
if (fallback_cpu == -1)
fallback_cpu = best_cpu;

And clarify this in the commit message.


thanks,

-Joel

[1] https://patchwork.kernel.org/patch/9884383/


>
>> Change from v5
>> -. exclude two patches already picked up by peterz
>> (sched/deadline: Make find_later_rq() choose a closer cpu in topology)
>> (sched/deadline: Change return value of cpudl_find())
>> -. apply what peterz fixed for 'prefer sibling', into deadline and rt
>>
>> Change from v4
>> -. remove a patch that might cause huge lock contention
>> (by spin lock(&cpudl.lock) in a hot path of scheduler)
>>
>> Change from v3
>> -. rename closest_cpu to best_cpu so that it align with rt
>> -. protect referring cpudl.elements with cpudl.lock
>> -. change return value of cpudl_find() to bool
>>
>> Change from v2
>> -. add support for SD_PREFER_SIBLING
>>
>> Change from v1
>> -. clean up the patch
>>
>> Byungchul Park (2):
>> sched/deadline: Add support for SD_PREFER_SIBLING on find_later_rq()
>> sched/rt: Add support for SD_PREFER_SIBLING on find_lowest_rq()
>>
>> kernel/sched/deadline.c | 46 +++++++++++++++++++++++++++++++++++++++++++---
>> kernel/sched/rt.c | 47 ++++++++++++++++++++++++++++++++++++++++++++---
>> 2 files changed, 87 insertions(+), 6 deletions(-)
>>
>> --
>> 1.9.1

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