Hello, In the context of perfmon (and the effort to merge it with mainline), I am looking at adding support for notification on idle. Basically, you can register a call back when entering the idle() loop and another callback when you leave. The callback is surrounding the lowest level of the idle loop, typically where you go low-power. The callback covers interrupts that get you out of idle. Why is this useful for perfmon? When measuring in system-wide, it is interesting to exclude the useless execution inside the idle loop. Originally, this meant not counting during the cycle-burning idle loop. However we are interested in measuring any interrupt triggered execution in the context of the idle loop. These days, there is no cycle burning loop anymore but rather the CPU goes into low power mode. That has an impact on the performance counters. Depending on the architecture, the PMU may be fully stopped, sometimes only certain counters are stopped (based on the event they measure), sometimes there are firmware bugs. In order to provide a uniform interface across all platforms, we could leverage the idle notification mechanism to explicitely start/stop monitoring when going in the lowest-level of the idle loop (i.e., low-power). This callback notification for idle already exists on x86-64. I am working on adding it to i386. I would need to add it to IA-64 as well. Looking at cpu_idle(), I see there is already some callback mechanism, with the mark_idle function pointer. It seems to be used only for the SGI machines. The way it is currently setup, the entry callback is invoked only when a task is blocking. I am not sure of the intent here. I am wondering if the existing callback could also work with the idle notification scheme. Any idea? -- -Stephane - To unsubscribe from this list: send the line "unsubscribe linux-ia64" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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