Re: [PATCH] Improvev netconsole support for RTL8139 NIC driver

[Jeff Garzik]

David Miller wrote:
> From: Jeff Garzik <jgarzik@xxxxxxxxx>
> Date: Tue, 25 Mar 2008 23:14:03 -0400
>
> > David Miller wrote:
> > > From: Jeff Garzik <jgarzik@xxxxxxxxx>
> > > Date: Tue, 25 Mar 2008 22:23:24 -0400
> > >
> > > > This is bogus -- you should never need to slow down the hot path in such 
> > > > a way.
> > > Slow down in what way?  Even on x86 saving the flags is just
> > > about as expensive as a plain sti/cli.
> > Replacing spin_lock() [current 8139too.c] with spin_lock_irqsave() 
> > results in a larger interrupt handler... more CPU instructions for the 
> > same result.
>
> Jeff, please be realistic.
>
> These interrupt handlers about to do a PIO on a status register, which
> will consume on the order of a few hundred cpu cycles.
>
> Counting an I-cache line or two, or 18 cycles here or there,
> is immaterial by comparison.

I am being realistic...  it's

* not needed
* increases code size
* increases number of CPU instructions executed
* not needed

Thus applying this consistency rule across N drivers needlessly 
increases the code size of N drivers.

Mainly I see such a change as a violation of a basic Linux principle: 
do what you must, and no more.

	Jeff



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