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SubjectRe: [PATCH] video: limit stack usage of ir-kbd-i2c.c
On Wed, 27 Feb 2008 11:23:26 +0100, Marcin Slusarz wrote:
> On Tue, Feb 26, 2008 at 11:23:20PM +0100, Jean Delvare wrote:
> > * You can move the handling of some ioctls to dedicated functions, just
> > like I did in i2c-dev:
> > http://lists.lm-sensors.org/pipermail/i2c/2008-February/003010.html
> > However there is a risk that gcc will inline these functions (that's
> > what happened to me...) Not sure how to prevent gcc from inlining.
>
> There's "noinline" attribute in linux/compiler.h (compiler-gcc.h actually)
> for these situations.

I didn't know about noinline, thanks for the tip. It works as expected,
however in the case of i2cdev_ioctl I'm not sure if it's worth it.
Without it, I have:

0x02ae i2cdev_ioctl [i2c-dev]: 192

With noinline, I have:

0x02ac i2cdev_ioctl_smbus [i2c-dev]: 112
0x05bc i2cdev_ioctl_rdrw [i2c-dev]: 112
0x087e i2cdev_ioctl [i2c-dev]: 32

32 + 112 = 144, 192 - 144 = only 48 bytes saved on the stack, at the
price of some performance loss. OTOH this makes the binary slightly
smaller (not sure why), which is always nice:

add/remove: 2/0 grow/shrink: 0/1 up/down: 1121/-1182 (-61)
function old new delta
i2cdev_ioctl_rdrw - 696 +696
i2cdev_ioctl_smbus - 425 +425
i2cdev_ioctl 1482 300 -1182

--
Jean Delvare


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