On Fri, 7 Apr 2017 11:43:49 +0200 Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote: > On Thu, Apr 06, 2017 at 10:31:46AM -0700, Linus Torvalds wrote: > > But maybe "monitor" is really cheap. I suspect it's microcoded, > > though, which implies "no". > > On my IVB-EP (will also try on something newer): > > MONITOR ~332 cycles > MWAIT ~224 cycles (C0, explicitly invalidated MONITOR) > > So yes, expensive. Interestingly, Intel optimization manual says: The latency of PAUSE instruction in prior generation microarchitecture is about 10 cycles, whereas on Skylake microarchitecture it has been extended to as many as 140 cycles. In another part this is claimed for efficiency improvement. Still much cheaper than your monitor+mwait on your IVB but if skylake is a bit faster it might become worth it.
