On Tue, Jan 06, 2015 at 10:53:35AM +1100, Cyril Bur wrote: > On Mon, 2015-01-05 at 11:50 -0500, Don Zickus wrote: > > cc'ing Marcelo > > > > On Mon, Dec 22, 2014 at 04:06:02PM +1100, Cyril Bur wrote: > > > When the hypervisor pauses a virtualised kernel the kernel will observe a > > > jump > > > in timebase, this can cause spurious messages from the softlockup > > > detector. > > > > > > Whilst these messages are harmless, they are accompanied with a stack > > > trace > > > which causes undue concern and more problematically the stack trace in the > > > guest has nothing to do with the observed problem and can only be > > > misleading. > > > > > > Futhermore, on POWER8 this is completely avoidable with the introduction > > > of > > > the Virtual Time Base (VTB) register. > > > > Hi Cyril, > > > > Your solution seems simple and doesn't disturb the softlockup code as much > > as the x86 solution does. The only small issue I had was the use of > > sched_clock instead of local_clock. I keep forgetting the difference > > (unstable clock is the biggest reason I think). > My apologies there it appears I stuffed up, local_clock was used > initially in the softlockup code, I'll send a v2.
Thanks! > > > Other than that, I am not the biggest fan of putting multiple virtual > > guest solutions for the same problem into the watchdog code. I would > > prefer a common solution/framework to leverage. > Agreed. > > > I have the x86 folks focusing on the steal_time stuff. It started with > > KVM and I believe VMWare is working on utilizing it too (and maybe Xen). > I'm not sure I've ever seen this, could you please point me towards > something I can look at? I am not too familar with it, but the kernel/watchdog.c code has calls to kvm_check_and_clear_guest_paused(), which is probably a good place to start. Cheers, Don > > > Not sure if that is useful or could be incoporated into the power8 code. > > Though to be honest I am curious if the steal_time code could be ported to > > your solution as it seems the watchdog code could remove all the > > steal_time warts. > Happy to help sus out the situation here, again, if you could pass on > what the x86 guys are working on, thanks. > > > Thanks, > > Cyril > > I have cc'd Marcelo into this discussion as he was the last person I > > remember talking with about this problem. > > > > Cheers, > > Don > > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
