linux-kernel - Re: [Cocci] [PATCH] Coccinelle: null: Optimise disjunctions in SmPL script “eno.cocci”

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Date:   Sun, 25 Oct 2020 19:28:01 +0100 (CET)
From:   Julia Lawall <julia.lawall@...ia.fr>
To:     Markus Elfring <Markus.Elfring@....de>
cc:     Coccinelle <cocci@...teme.lip6.fr>,
        Gilles Muller <Gilles.Muller@...6.fr>,
        Michal Marek <michal.lkml@...kovi.net>,
        Nicolas Palix <nicolas.palix@...g.fr>,
        kernel-janitors@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [Cocci] [PATCH] Coccinelle: null: Optimise disjunctions in SmPL script “eno.cocci”

On Sun, 25 Oct 2020, Markus Elfring wrote:

> From: Markus Elfring <elfring@...rs.sourceforge.net>
> Date: Sun, 25 Oct 2020 18:54:36 +0100
>
> A disjunction is applied by this script for the semantic patch language.
> This construct uses short-circuit evaluation. It has got the consequence
> that the last element of the specified condition will only be checked
> if all previous parts did not match. Such a technical detail leads to
> a recommended ordering of condition parts if you would like to care for
> optimal run time characteristics of SmPL code.
>
> An usage incidence was determined for the specified identifiers in source
> files from the software “Linux next-20201023” by another SmPL script.
>
> See also:
> Determination of an usage statistic for memory allocation calls
> https://lore.kernel.org/cocci/2774601.u91sIFNy1E@sonne/
>
> This analysis result indicates a clear ranking for such function calls.
> Thus reorder the SmPL disjunction items according to their usage incidence.

Did you actually test this before and after the change and see a
difference in performance?  On my laptop, I see absolutely no difference,
for the patch mode and for the context mode.  I didn't try the other
cases.

Before the change:

patch: 440.182u 2.049s 1:53.12 390.9%	0+0k 0+232io 4pf+0w
context: 392.931u 2.164s 1:41.53 389.1%	0+0k 432+360io 5pf+0w

After the change:

patch: 442.182u 2.090s 1:54.13 389.2%	0+0k 0+240io 4pf+0w
context: 392.742u 2.035s 1:41.37 389.4%	0+0k 0+360io 4pf+0w

julia

>
> Signed-off-by: Markus Elfring <elfring@...rs.sourceforge.net>
> ---
>  scripts/coccinelle/null/eno.cocci | 15 +++++++++++----
>  1 file changed, 11 insertions(+), 4 deletions(-)
>
> diff --git a/scripts/coccinelle/null/eno.cocci b/scripts/coccinelle/null/eno.cocci
> index 81584ff87956..969cab5116a9 100644
> --- a/scripts/coccinelle/null/eno.cocci
> +++ b/scripts/coccinelle/null/eno.cocci
> @@ -17,8 +17,16 @@ virtual report
>  @depends on patch@
>  expression x,E;
>  @@
> -
> -x = \(kmalloc\|kzalloc\|kcalloc\|kmem_cache_alloc\|kmem_cache_zalloc\|kmem_cache_alloc_node\|kmalloc_node\|kzalloc_node\)(...)
> + x =
> +(kzalloc
> +|kmalloc
> +|kcalloc
> +|kmem_cache_alloc
> +|kmem_cache_zalloc
> +|kzalloc_node
> +|kmalloc_node
> +|kmem_cache_alloc_node
> +)(...)
>  ... when != x = E
>  - IS_ERR(x)
>  + !x
> @@ -27,8 +35,7 @@ x = \(kmalloc\|kzalloc\|kcalloc\|kmem_cache_alloc\|kmem_cache_zalloc\|kmem_cache
>  expression x,E;
>  position p1,p2;
>  @@
> -
> -*x = \(kmalloc@p1\|kzalloc@p1\|kcalloc@p1\|kmem_cache_alloc@p1\|kmem_cache_zalloc@p1\|kmem_cache_alloc_node@p1\|kmalloc_node@p1\|kzalloc_node@p1\)(...)
> +*x = \(kzalloc@p1\|kmalloc@p1\|kcalloc@p1\|kmem_cache_alloc@p1\|kmem_cache_zalloc@p1\|kzalloc_node@p1\|kmalloc_node@p1\|kmem_cache_alloc_node@p1\)(...)
>  ... when != x = E
>  * IS_ERR@p2(x)
>
> --
> 2.29.1
>
> _______________________________________________
> Cocci mailing list
> Cocci@...teme.lip6.fr
> https://systeme.lip6.fr/mailman/listinfo/cocci
>

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