linux-kernel - Re: [PATCH v2] sched: Micro optimization in pick_next_task() and in check_preempt

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Date:   Thu, 19 Dec 2019 10:40:18 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Kirill Tkhai <ktkhai@...tuozzo.com>
Cc:     Peter Zijlstra <peterz@...radead.org>, mingo@...hat.com,
        juri.lelli@...hat.com, vincent.guittot@...aro.org,
        dietmar.eggemann@....com, bsegall@...gle.com, mgorman@...e.de,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] sched: Micro optimization in pick_next_task() and in
 check_preempt_curr()

On Thu, 19 Dec 2019 18:20:58 +0300
Kirill Tkhai <ktkhai@...tuozzo.com> wrote:

> From: Kirill Tkhai <ktkhai@...tuozzo.com>
> 
> This introduces an optimization based on xxx_sched_class addresses
> in two hot scheduler functions: pick_next_task() and check_preempt_curr().
> 
> After this patch, it will be possible to compare pointers to sched classes
> to check, which of them has a higher priority, instead of current iterations
> using for_each_class().
> 
> One more result of the patch is that size of object file becomes a little
> less (excluding added BUG_ON(), which goes in __init section):
> 
> $size kernel/sched/core.o
>          text     data      bss	    dec	    hex	filename
> before:  66446    18957	    676	  86079	  1503f	kernel/sched/core.o
> after:   66398    18957	    676	  86031	  1500f	kernel/sched/core.o
> 
> SCHED_DATA improvements guaranteeing order of sched classes are made
> by Steven Rostedt <rostedt@...dmis.org>

For the above changes, you can add:

Signed-off-by: Steven Rostedt (VMware) <rostedt@...dmis.org>

-- Steve

> 
> Signed-off-by: Kirill Tkhai <ktkhai@...tuozzo.com>
> 
> v2: Steven's data sections ordering. Hunk with comment in Makefile is removed.
> ---
>  include/asm-generic/vmlinux.lds.h |    8 ++++++++
>  kernel/sched/core.c               |   24 +++++++++---------------
>  kernel/sched/deadline.c           |    3 ++-
>  kernel/sched/fair.c               |    3 ++-
>  kernel/sched/idle.c               |    3 ++-
>  kernel/sched/rt.c                 |    3 ++-
>  kernel/sched/stop_task.c          |    3 ++-
>  7 files changed, 27 insertions(+), 20 deletions(-)
> 
> diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
> index e00f41aa8ec4..ff12a422ff19 100644
> --- a/include/asm-generic/vmlinux.lds.h
> +++ b/include/asm-generic/vmlinux.lds.h
> @@ -108,6 +108,13 @@
>  #define SBSS_MAIN .sbss
>  #endif
>