linux-kernel - Re: [PATCH v2] sched/deadline: Make find_later

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Date:   Tue, 21 Mar 2017 14:28:50 +0100
From:   Daniel Bristot de Oliveira <bristot@...hat.com>
To:     Byungchul Park <byungchul.park@....com>, peterz@...radead.org,
        mingo@...nel.org
Cc:     linux-kernel@...r.kernel.org, juri.lelli@...il.com,
        rostedt@...dmis.org, kernel-team@....com
Subject: Re: [PATCH v2] sched/deadline: Make find_later_rq() choose a closer
 cpu in topology

On 03/21/2017 08:52 AM, 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.

That is a nice patch! But I wonder what would be the behavior with your
patch in the following hw:

# numactl --hardware
available: 2 nodes (0-1)
node 0 cpus: 0 2 4 6 8 10 12 14
node 0 size: 16159 MB
node 0 free: 15308 MB
node 1 cpus: 1 3 5 7 9 11 13 15
node 1 size: 16384 MB
node 1 free: 15028 MB
node distances:
node   0   1
  0:  10  21
  1:  21  10

-- Daniel