Re: [PATCH] genirq: ARM dyntick cleanup

[Russell King <rmk+lkml@arm.linux.org.uk>]

On Mon, Jul 03, 2006 at 12:55:42AM -0700, Andrew Morton wrote:
> On Mon, 3 Jul 2006 08:41:55 +0100
> Russell King <rmk+lkml@arm.linux.org.uk> wrote:
> 
> > On Sun, Jul 02, 2006 at 05:35:27PM -0700, Andrew Morton wrote:
> > > This is not exactly a thing of beauty either.  It's much cleaner to use
> > > __attribute__((weak)), but that will add an empty call-return to everyone's
> > > interrupts.
> > 
> > Let's not go overboard with the weak stuff - it does not get removed
> > at link time, so it remains as dead code in the kernel image.
> 
> Well.
> 
> void handle_dynamic_tick(struct irqaction *action)
> {
> }
> 
> consumes one byte, doesn't it?  That's not very far overboard ;)

ROTFL!

All the word isn't x86.  On ARM it's 3 words for the stack setup and
one for the tear down, so 16 bytes, assuming the function doesn't
return a value.  If it does, add another 4 bytes.

So, on ARM potentially 16 to 20 bytes per weak function.  That's a
1600% to 2000% increase on your estimate.

(Unfortunately we have to tell the compiler to always generate stack
frames otherwise we can't get call traces out of the kernel.)

-- 
Russell King
 Linux kernel    2.6 ARM Linux   - http://www.arm.linux.org.uk/
 maintainer of:  2.6 Serial core