Hi,
On Wed, Sep 08, 2004 at 07:21:06PM +1000, Con Kolivas wrote:
> Andreas Mohr wrote:
> >Some more explanation:
> >AFAIK unlikely() should only be used when you're damn sure that this will
> >NEVER occur (e.g. failure cases), since it will artificially aggravate
> >penalty of this check in case it does occur.
> >IRQ sharing is *much* too common to justify using unlikely() here.
> >*ESPECIALLY* since IRQ sharing is very latency critical!
>
> The magnitude of it's effect is overstated somewhat. Firstly we're
> talking about a delay in the nanosecond range, and second the cpu will
> optimise that out if it finds it's a frequently used path. Despite all
> that, however, I agree it's probably inappropriate. {un}likely() should
> be used for a path that is always/never traversed except in fault
> handling, jiffy wrap etc.
True, it shouldn't make too much of a difference.
BTW, I just checked linux-2.6.8.1/sound/pci/intel8x0.c ,
and to me it seems it doesn't take IRQ sharing into account at all.
Would it be useful to carefully optimize many IRQ handlers for IRQ sharing
and send you a patch for inclusion in -ck?
Andreas Mohr
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