On Tue, Nov 27, 2007 at 02:22:03AM -0800, Bill Broadley wrote: > Hrm, why? Does context switches not scale with core speed? Or number > of cores? Can't interrupts be spread across CPUs?
No, no, no, and kinda. Caches and main memory access cause problems. There's a reason why high speed networks eschew interrupts. Haven't you ever noticed that your InfiniPath cards rarely show any interrupts? OK, 2 to bring the link up at boot, but MPI doesn't generate any. In the disk case, every context switch is an opportunity to dirty the wrong cache. And accessing data from someone else's cache is slower than going to main memory, and on NUMA machines like the Opteron, the wrong main memory is slower than the local main memory. And round-robining your interrupts, well, that's a recipe for disaster. > If you > need to install a 48 disk server at the top of a 48U rack I am definitely > busy ;-). They make lifts for this situation ;-) (plus you have a steady supply of undergraduates!) -- greg _______________________________________________ Beowulf mailing list, [email protected] To change your subscription (digest mode or unsubscribe) visit http://www.beowulf.org/mailman/listinfo/beowulf
