Re: [Qemu-devel] Fedora FC21 - Bug: 100% CPU and hangs in gettimeofday(&tp, NULL); forever

[Paolo Bonzini]

On 13/01/2015 22:14, Gerhard Wiesinger wrote:
> 
> I also had a look at the kernel code again:
> http://lxr.free-electrons.com/source/kernel/time/timekeeping.c?v=3.17#L493
> 499         do {
> 500                 seq = read_seqcount_begin(&tk_core.seq);
> 501
> 502                 ts->tv_sec = tk->xtime_sec;
> 503                 nsecs = timekeeping_get_ns(&tk->tkr);
> 504
> 505         } while (read_seqcount_retry(&tk_core.seq, seq));
> 
> So it looks like that the seqcount always changes and therefore loops
> forever here (as far as I digged it down this is the only loop here).
> 
> Might be something wrong with the memory barriers in recent qemu-kvm
> releases?

No, that's not possible.  Unless you pause/resume or migrate the VM, all
of the handling of kvmclock is entirely in the kernel.

Paolo