Messages in this thread | | | Subject | Re: kernel optimization | From | Alan Cox <> | Date | Sat, 23 Jul 2005 20:50:36 +0100 |
| |
On Sad, 2005-07-23 at 02:30 -0400, cutaway@bellsouth.net wrote: > Larger does not always mean slower. If it did, nobody would implement a > loop unrolling optimization.
Generally speaking nowdays it does. Almost all loop unrolls are a loss on PIV.
> ex. Look at how GCC generates jump tables for switch() when there's about > 10-12 (or more) case's sparsely scattered in the rage from 0 through 255.
You are comparing with very expensive jump operations its an unusual case. For the majority of situations the TLB/cache overhead of misses vastly outweighs the odd clock cycle gained by verbose output.
- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |