On 09.02.2018 14:49, Luiz Capitulino wrote: > On Fri, 9 Feb 2018 08:56:19 +0100 > Viktor Mihajlovski <mihaj...@linux.vnet.ibm.com> wrote: > >> On 08.02.2018 21:33, Eduardo Habkost wrote: >>> On Thu, Feb 08, 2018 at 11:17:32AM -0500, Luiz Capitulino wrote: >>> [...] >>>> The "halted" field is somewhat controversial. On the one hand, >>>> it offers a convenient way to know if a guest CPU is idle or >>>> running. On the other hand, it's a field that can change many >>>> times a second. In fact, the halted state can change even >>>> before query-cpus-fast has returned. This makes one wonder if >>>> this field should be dropped all together. Having the "halted" >>>> field as optional gives a better option for dropping it in >>>> the future, since we can just stop returning it. >>> >>> I'd just drop it, unless we find a use case where it's really >>> useful. > > I don't think there's any, unless for debugging purposes. > > I'm keeping it mainly for s390. Viktor, libvirt is still using > this field in s390, no? see below > > Dropping halted and having management software still using query-cpus > because of halted would be a total failure of query-cpus-fast. > >>> Also, the code that sets/clears cpu->halted is target-specific, >>> so I wouldn't be so sure that simply checking for >>> !kvm_irqchip_in_kernel() is enough on all targets. > > I checked the code and had the impression it was enough, but > I don't have experience with other archs. So, would be nice > if other archs maintainers could review this. I'll try to ping them. > >> Right, the present patch effectively disables halted anyway (including >> s390). > > No, it doesn't. It only disables halted for archs that require going > to the kernel to get it.> >> So it may be cleaner to just drop it right now. >> Assuming the presence of architecure-specific data, libvirt can derive a >> halted state (or an equivalent thereof) from query-cpus-fast returned >> information. > > This is a different proposal. You're proposing moving the halted state > to a CPU-specific field. This is doable if that's what we want. > In order to use query-cpus-fast, libvirt has to change code anyway. Since libvirt is only providing cpu.n.halted for s390, and this value can be derived from the cpu-state, there's no need for QEMU to return halted in query-cpus-fast any more.
-- Regards, Viktor Mihajlovski
