linux-kernel - [PATCH v8 0/2] Make find_later_rq() choose a closer cpu in topology

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Message-Id: <1503044519-2804-1-git-send-email-byungchul.park@lge.com>
Date:   Fri, 18 Aug 2017 17:21:57 +0900
From:   Byungchul Park <byungchul.park@....com>
To:     peterz@...radead.org, mingo@...nel.org
Cc:     joel.opensrc@...il.com, linux-kernel@...r.kernel.org,
        juri.lelli@...il.com, rostedt@...dmis.org, kernel-team@....com
Subject: [PATCH v8 0/2] Make find_later_rq() choose a closer cpu in topology

Thanks to Joel, I could fix a typo and simplify code more.

-----8<-----

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.

Change from v7
   -. fix a trivial typo
   -. modify commit messages to explain what it does more clearly
   -. simplify code with an existing macro

Change from v6
   -. add a comment about selection of fallback_cpu incase more than one exist
   -. modify a comment explaining what we do wrt PREFER_SIBLING

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 | 55 +++++++++++++++++++++++++++++++++++++++++++++---
 kernel/sched/rt.c       | 56 ++++++++++++++++++++++++++++++++++++++++++++++---
 2 files changed, 105 insertions(+), 6 deletions(-)

-- 
1.9.1