On 10/23/2012 4:49 AM, Jon Hunter wrote: > Therefore, I believe it will improve search time and hence, boot time if > we have interrupt-parent defined in each node. I strongly suspect (based on many years of performance tuning, with special focus on boot time) that the time difference will be completely insignificant. The total extra time for walking up the interrupt tree for every interrupt in a large system is comparable to the time it takes to send a few characters out a UART. So you can get more improvement from eliminating a single printk() than from globally adding per-node interrupt-parent. Furthermore, the cost of processing all of the interrupt-parent properties is probably similar to the cost of the avoided tree walks. CPU cycles are very fast compared to I/O register accesses, say a factor of 100. Now consider that many modern devices contain embedded microcontrollers (SD cards, network interface modules, USB hubs and devices, ...), and those devices usually require various delays measured in milliseconds, to ensure that the microcontroller is ready for the next initialization step. Those delays are extremely long compared to CPU cycles. Obviously, some of that can be overlapped by careful multithreading, but that isn't free either. The bottom line is that I'm pretty sure that adding per-node interrupt-parent would not be worthwhile from the standpoint of speeding up boot time. -- To unsubscribe from this list: send the line "unsubscribe linux-omap" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
