linux-kernel - Re: First kernel patch (optimization)

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Message-ID: <CAJJ6jxsv_RZdXdRjqJzHGJqySkwNGitzO1gQ=tMCVy56FMWNjg@mail.gmail.com>
Date:	Tue, 15 Sep 2015 17:09:03 -0700
From:	Steve Calfee <stevecalfee@...il.com>
To:	Eric Curtin <ericcurtin17@...il.com>
Cc:	Valentina Manea <valentina.manea.m@...il.com>,
	shuah.kh@...sung.com, USB list <linux-usb@...r.kernel.org>,
	Kernel development list <linux-kernel@...r.kernel.org>
Subject: Re: First kernel patch (optimization)

On Tue, Sep 15, 2015 at 12:53 PM, Eric Curtin <ericcurtin17@...il.com> wrote:
> Signed-off-by: Eric Curtin <ericcurtin17@...il.com>
>
> diff --git a/tools/usb/usbip/src/usbip_detach.c b/tools/usb/usbip/src/usbip_detach.c
> index 05c6d15..9db9d21 100644
> --- a/tools/usb/usbip/src/usbip_detach.c
> +++ b/tools/usb/usbip/src/usbip_detach.c
> @@ -47,7 +47,9 @@ static int detach_port(char *port)
>         uint8_t portnum;
>         char path[PATH_MAX+1];
>
> -       for (unsigned int i = 0; i < strlen(port); i++)
> +       unsigned int port_len = strlen(port);
> +
> +       for (unsigned int i = 0; i < port_len; i++)
>                 if (!isdigit(port[i])) {
>                         err("invalid port %s", port);
>                         return -1;
>
> --

Hi Eric,

This is fine, but what kind of wimpy compiler optimizer will not move
the constant initializer out of the loop? I bet if you compare binary
sizes/code it will be exactly the same, and you added some characters
of code. Reorganizing code for readability is fine, but for compiler
(in)efficiency seems like a bad idea.

Regards, Steve
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