On 06/23/2013 02:29 PM, Linus Torvalds wrote:
You could try to do that either *in* the idle thread (which would take the context switch overhead - maybe negating some of the advantages), or alternatively hook into the scheduler idle logic before actually doing the switch. But anything that starts polling when there are other runnable processes to be done sounds really debatable. Even if it's "only" 5us or so. There's a lot of real work that could be done in 5us.
Having a hook into the idle code could be useful for KVM, too. In certain message passing workloads, we have seen that the system throughput suffers greatly simply by having the KVM thread's preempt notifiers save CPU state when the guest goes idle, and re-load it when the guest VCPU is activated again. Avoiding the context switch overhead when nothing else wants to run, but being immediately preempted when something does, could be a big win. Would it make sense to have some hook that says "I *am* an idle thread right now", as opposed to "context switch to the idle thread"? That hook could even run the cpuidle code, and switch to the real idle task (saving the current task state), and put the CPU into a C-state, when the expected sleep time is long... -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
