On 14/03/2017 17:58, Radim Krčmář wrote: >> I assume there's a good reason why we call guest_enter() and >> guest_exit() in the hot path on every KVM architecture? > I consider myself biased when it comes to jiffies, so no judgement. :) > > From what I see, the mode switch is used only for statistics. vtime is only for statistics, but guest_enter/exit are important because they enter an RCU extended quiescent state. This means that (physical) CPUs running a guest are effectively "off" from the point of view of the RCU accounting machinery. Not having to perform any RCU work is very good for jitter. Paolo
