* H. Peter Anvin <hpa@xxxxxxxxx> wrote: > On 01/20/2014 01:16 AM, Peter Zijlstra wrote: > >> > >> The difference is the STI! > > > > So do the local_irq_enable(); mwait_idle_with_hints(0,0); thing. > > > > No, that doesn't work. The point of __sti_mwait() is that the STI > is the instruction immediately before the MWAIT, just like the > combination STI;HLT. Since the execution of STI is always delayed > by one instruction, these two instructions form an atomic unit, > which means interrupts are enabled "after" we have entered MWAIT or > HLT. > > > But that's entirely different from saying that core2 doesn't > > support mwait_idle_with_hints because its a different instruction. > > If you think of STI;MWAIT as a "compound instruction" it kind of is. > Newer CPUs don't have to play that trick anymore, because there is a > flag to MWAIT which breaks us out of MWAIT on a pending interrupt > without having to actually enable interrupts at the point of the > MWAIT. As a side note, at minimum the semantic and compatibility difference needs to be _very_ clearly present in the naming. Something like mwait_old_() or mwait_core2_(). That way such dependencies and assumptions don't get lost in code restructuring, etc. Thanks, Ingo -- To unsubscribe from this list: send the line "unsubscribe linux-next" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
