2016-10-26 22:01 GMT+08:00 Radim Krčmář <rkrcmar@xxxxxxxxxx>: > 2016-10-26 14:08+0800, Wanpeng Li: >> 2016-10-26 14:02 GMT+08:00 Wanpeng Li <kernellwp@xxxxxxxxx>: >>> 2016-10-25 19:43 GMT+08:00 Radim Krčmář <rkrcmar@xxxxxxxxxx>: >>>> I will have some comments, because it would be nicer if it measured the >>>> latency ... expected_expiration is not computed correctly. >>> >>> It measured the latency from guest programs the clock event device to >>> interrupt injected to guest after timer fire. > > No. It never computed the time when the timer fires, the test measured > the duration of the period. > > Imagine that the dashed line below is a timeline. Pipe is idealized > firing of the periodic timer and caret is the time when the guest read > time in the interrupt. The number below caret is the latency. > > The period is 7. > > -------------------------------------------- > | | | | | | | > ^ ^ ^ ^ ^ ^ ^ > 1 2 3 1 2 1 1 > > The test would report "latencies" as: > > 1 1 1 -2 1 -1 0 > > because it used now() + period to compute the next expected expiration > > Similarly in this case, > -------------------------------------------- > | | | | | | | > ^ ^ ^ ^ ^ ^ > 6 6 6 6 6 6 > > The latency is always 6, but the test would report > > 6 0 0 0 0 0 > > And if we improved the latency by 1, you'd only see the difference in > the first number. The test measured the duration of the period. Agreed, thanks for the details. :) Regards, Wanpeng Li -- 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
