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

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Message-ID: <af65cbaf-2f8e-0384-03e8-262d35e3790e@virtuozzo.com>
Date:   Thu, 19 Dec 2019 19:08:05 +0300
From:   Kirill Tkhai <ktkhai@...tuozzo.com>
To:     Steven Rostedt <rostedt@...dmis.org>
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 19.12.2019 18:40, Steven Rostedt wrote:
> 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>

Should I resend this as two patches, with your changes in a separate?

> 
>>
>> 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
>>