linux-kernel - Re: [PATCH] scripts: coccinelle: check for !(un)?likely usage

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Date:   Mon, 26 Aug 2019 00:19:34 +0300
From:   Denis Efremov <efremov@...ux.com>
To:     Joe Perches <joe@...ches.com>, cocci@...teme.lip6.fr
Cc:     linux-kernel@...r.kernel.org, Julia Lawall <Julia.Lawall@...6.fr>,
        Gilles Muller <Gilles.Muller@...6.fr>,
        Nicolas Palix <nicolas.palix@...g.fr>,
        Michal Marek <michal.lkml@...kovi.net>
Subject: Re: [PATCH] scripts: coccinelle: check for !(un)?likely usage

> I think it's incorrect to say so in general. For example, on x86/64:
> 
> $ make mrproper
> $ make allyesconfig
> $ make && mv vmlinux vmlinux-000
> $ make coccicheck MODE=patch COCCI=scripts/coccinelle/misc/unlikely.cocci | patch -p1
> $ make 
> $ ./scripts/bloat-o-meter ./vmlinux-000 ./vmlinux
> add/remove: 0/0 grow/shrink: 3/4 up/down: 41/-35 (6)
> Function                                     old     new   delta
> dpaa2_io_service_rearm                       357     382     +25
> intel_pmu_hw_config                         1277    1285      +8
> get_sigframe.isra.constprop                 1657    1665      +8
> csum_partial_copy_from_user                  605     603      -2
> wait_consider_task                          3807    3797     -10
> __acct_update_integrals                      384     373     -11
> pipe_to_sendpage                             459     447     -12
> Total: Before=312759461, After=312759467, chg +0.00%
> 
> It definitely influence the way the compiler optimizes the code.  

Small addition:

Results with allyesconfig and KCOV, KASAN, KUBSAN, FTRACE, TRACE_BRANCH_PROFILING,
PROFILE_ALL_BRANCHES disabled:
./scripts/bloat-o-meter ./vmlinux-000 ./vmlinux
add/remove: 0/0 grow/shrink: 2/3 up/down: 22/-22 (0)
Function                                     old     new   delta
i40e_xmit_xdp_ring                           457     477     +20
__acct_update_integrals                      127     129      +2
csum_partial_copy_from_user                  208     207      -1
dpaa2_io_service_rearm                       180     177      -3
wait_consider_task                          1338    1320     -18

For defconfig:
./scripts/bloat-o-meter ./vmlinux-000 ./vmlinux 
add/remove: 0/0 grow/shrink: 3/1 up/down: 16/-5 (11)
Function                                     old     new   delta
do_signal                                   1513    1521      +8
wait_consider_task                          2151    2157      +6
__acct_update_integrals                      127     129      +2
csum_partial_copy_from_user                  223     218      -5

Denis