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

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Date:   Wed, 22 Mar 2017 11:46:20 +0900
From:   Byungchul Park <byungchul.park@....com>
To:     Daniel Bristot de Oliveira <bristot@...hat.com>
CC:     <peterz@...radead.org>, <mingo@...nel.org>,
        <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 Tue, Mar 21, 2017 at 02:28:50PM +0100, Daniel Bristot de Oliveira wrote:
> 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

Hi,

In this case, I guess the topology looks like:

    0 --+
        +--+
    2 --+  |
           +-- ... --+
    4 --+  |         |
        +--+         |
    6 --+            |

    ...             ...

     9 --+           |
         +--+        |
    11 --+  |        |
            +-- ... -+
    13 --+  |
         +--+
    15 --+

And sched_domain would also reflect that. So the dl's push works well.
Do I miss something?

In addition, IMHO, it's not an issue for dl's push but one for building
sched_domains. Wrong?

Thanks,
Byungchul