On Sun, May 22, 2016 at 6:26 PM, Yang Zhang <yang.zhang.wz@xxxxxxxxx> wrote: > On 2016/5/21 2:37, David Matlack wrote: >> >> It's not obvious to me why polling for a timer interrupt would improve >> context switch latency. Can you explain a bit more? > > > We have a workload which using high resolution timer(less than 1ms) inside > guest. It rely on the timer to wakeup itself. Sometimes the timer is > expected to fired just after the VCPU is blocked due to execute halt > instruction. But the thread who is running in the CPU will turn off the > hardware interrupt for long time due to disk access. This will cause the > timer interrupt been blocked until the interrupt is re-open. Does this happen on the idle thread (swapper)? If not, halt-polling may not help; it only polls if there are no other runnable threads. > For optimization, we let VCPU to poll for a while if the next timer will > arrive soon before schedule out. And the result shows good when running > several workloads inside guest. Thanks for the explanation, I appreciate it. > > -- > best regards > yang -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
