linux-kernel - Re: [PATCH 1/4] sched: make nr

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Message-ID: <YJ2YphIIwMEQ5mIh@localhost.localdomain>
Date:   Fri, 14 May 2021 00:22:46 +0300
From:   Alexey Dobriyan <adobriyan@...il.com>
To:     Ingo Molnar <mingo@...nel.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>, mingo@...hat.com,
        Borislav Petkov <bp@...en8.de>, linux-kernel@...r.kernel.org,
        x86@...nel.org, Linus Torvalds <torvalds@...ux-foundation.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH 1/4] sched: make nr_running() return 32-bit

On Thu, May 13, 2021 at 11:58:38AM +0200, Ingo Molnar wrote:
> 
> * Thomas Gleixner <tglx@...utronix.de> wrote:
> 

> > Just with the default config for one of my reference machines:
> > 
> >    text		data	bss	dec	 hex	 filename
> > 16679864	6627950	1671296	24979110 17d26a6 ../build/vmlinux-before
> > 16679894	6627950	1671296	24979140 17d26c4 ../build/vmlinux-after
> > ------------------------------------------------------------------------
> >      +30
> 
> Using '/usr/bin/size' to compare before/after generated code is the wrong 
> way to measure code generation improvements for smaller changes due to 
> default alignment creating a reserve of 'padding' bytes at the end of most 
> functions. You have to look at the low level generated assembly directly.

This is bloat-o-meter output with Fedora 33 .config:

This is how they look like, something gets bigger but total is smaller
(otherwise why would I send it). Apparently something got one 1 byte too
many and pushed padding.

add/remove: 0/0 grow/shrink: 6/21 up/down: 18/-42 (-24)
Function                                     old     new   delta
calc_load_fold_active                         50      56      +6
calc_load_nohz_start                         100     103      +3
calc_load_nohz_remote                         85      88      +3
calc_global_load_tick                         86      89      +3
pull_dl_task                                 901     903      +2
switched_from_dl                             613     614      +1
update_rt_migration                          165     164      -1
update_dl_migration                          141     140      -1
ttwu_do_activate                             181     180      -1
tick_nohz_idle_exit                          225     224      -1
tick_irq_enter                               227     226      -1
print_rt_rq.cold                             238     237      -1
print_rt_rq                                  413     412      -1
nr_iowait_cpu                                 31      30      -1
init_rt_rq                                   143     142      -1
show_stat                                   1745    1743      -2
nr_running                                    75      73      -2
nr_iowait                                     83      81      -2
get_cpu_iowait_time_us                       260     258      -2
get_cpu_idle_time_us                         260     258      -2
find_lock_later_rq                           507     505      -2
enqueue_task_rt                              777     775      -2
enqueue_task_dl                             2461    2459      -2
dequeue_rt_stack                             576     574      -2
menu_select                                 1492    1489      -3
__dequeue_dl_entity                          419     414      -5
init_dl_rq                                    88      81      -7
Total: Before=25729849, After=25729825, chg -0.00%