linux-kernel - Re: [PATCH v5 0/4] Make find_later_rq() choose a closer cpu in topology

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Message-ID: <20170602021913.GC3623@X58A-UD3R>
Date:   Fri, 2 Jun 2017 11:19:13 +0900
From:   Byungchul Park <byungchul.park@....com>
To:     peterz@...radead.org, mingo@...nel.org
Cc:     linux-kernel@...r.kernel.org, juri.lelli@...il.com,
        rostedt@...dmis.org, bristot@...hat.com, kernel-team@....com
Subject: Re: [PATCH v5 0/4] Make find_later_rq() choose a closer cpu in
 topology

On Tue, May 23, 2017 at 11:00:55AM +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.

Hi, Peterz,

I wonder if you remember what I answered your question about applying
this approach into rt policy. Rt *already* works as expected.

And I implemented what you suggested, SD_PREFER_SIBLING. It would be
appriciated to check if I works correctly.

Thank you,
Byungchul

> 
> 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 (4):
>   sched/deadline: Make find_later_rq() choose a closer cpu in topology
>   sched/deadline: Change return value of cpudl_find()
>   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/cpudeadline.c | 26 ++++++++++++-------------
>  kernel/sched/deadline.c    | 48 +++++++++++++++++++++++++++++++---------------
>  kernel/sched/rt.c          | 17 ++++++++++++++++
>  3 files changed, 63 insertions(+), 28 deletions(-)
> 
> -- 
> 1.9.1