On Thu, 4 Sep 2014, Paolo Bonzini wrote: > Il 04/09/2014 22:58, Thomas Gleixner ha scritto: > > This is simply wrong. > > It is. > > > Now I have no idea why you think it needs to add xtime_sec. If the > > result is wrong, then we need to figure out which one of the supplied > > values is wrong and not blindly add xtime_sec just because that makes > > it magically correct. > > > > Can you please provide a proper background why you think that adding > > xtime_sec is a good idea? > > It's not a good idea indeed. I didn't fully digest the 3.16->3.17 > timekeeping changes and messed up this patch. > > However, there is a bug in the "base_mono + offs_boot" formula, given > that: > > - bisection leads to the merge commit of John's timers branch > > - bisecting within John's timers branch, with a KVM commit on top to > make the code much easier to trigger, leads to commit cbcf2dd3b3d4 > (x86: kvm: Make kvm_get_time_and_clockread() nanoseconds based, > 2014-07-16). > > - I backported your patch to 3.16, using wall_to_monotonic + > total_sleep_time + xtime_sec (wtm+xtime_sec as in pre-cbcf2dd3b3d4 > code, total_sleep_time from 3.16 monotonic_to_bootbased) and it works > > - In v2 of the patch I fixed the bug by changing the formula > "base_mono + offs_boot" to "offs_boot - offs_real" (and then adding > xtime_sec separately as in the 3.16 backport), but the two formulas > "base_mono + offs_boot" and "offs_boot - offs_real + xtime_sec" ought > to be identical. > > I find "offs_boot - offs_real + xtime" more readable than the > alternative "base_mono + offs_boot + xtime_nsec", so the fix doubles as > a cleanup for me and I'm fine with it. But something must be wrong in > the timekeeping code. I think I have a vague idea what happened, but I'm way too tired now to write it up fully. I'll do that tomorrow morning with brain awake. Thanks, tglx -- 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
