linux-kernel - Re: [PATCH 3/4] gpio: sysfs: don't use sprintf() for 'value' attribute

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Message-ID: <CACRpkdZ1mVVzf9wyGx3_oZm=3mqk4ynBg1RidFcV5NBXuK1iAg@mail.gmail.com>
Date:   Wed, 20 Dec 2017 10:34:29 +0100
From:   Linus Walleij <linus.walleij@...aro.org>
To:     Christophe Leroy <christophe.leroy@....fr>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        linux-gpio@...r.kernel.org
Subject: Re: [PATCH 3/4] gpio: sysfs: don't use sprintf() for 'value' attribute

On Mon, Dec 18, 2017 at 11:08 AM, Christophe Leroy
<christophe.leroy@....fr> wrote:

> A bench with 'perf record' shows that most of time spent in value_show()
> is spent in sprintf()
>
> --42.41%--sysfs_kf_read
>           |
>           |--39.73%--dev_attr_show
>           |          |
>           |          |--38.23%--value_show
>           |          |          |
>           |          |          |--29.22%--sprintf
>           |          |          |
>           |          |          |--2.94%--gpiod_get_value_cansleep
>           |          |          |
>
> value_show() only returns "0\n" or "1\n", therefore the use of
> sprintf() can be avoided
>
> With this patch we get the following result with 'perf record'
>
> --13.89%--sysfs_kf_read
>           |
>           |--10.72%--dev_attr_show
>           |          |
>           |          |--9.44%--value_show
>           |          |          |
>           |          |          |--4.61%--gpiod_get_value_cansleep
>
> Signed-off-by: Christophe Leroy <christophe.leroy@....fr>

Patch applied.

Yours,
Linus Walleij