Hi Mykyta, > On 4 Feb 2026, at 13:58, Mykyta Poturai <[email protected]> wrote: > > On 03.02.26 18:35, Bertrand Marquis wrote: >> Hi Mykyta, >> >>> On 13 Jan 2026, at 09:45, Mykyta Poturai <[email protected]> wrote: >>> >>> This series implements support for CPU hotplug/unplug on Arm. To achieve >>> this, >>> several things need to be done: >>> >>> 1. XEN_SYSCTL_CPU_HOTPLUG_* calls implemented on Arm64. >>> 2. Enabled building of xen-hptool. >>> 3. Migration of irqs from dying CPUs implemented. >>> >>> Tested on QEMU. >> >> Do you have a way to validate this on real hardware ? >> Doing hotplug/unplug might have side effects (caches, coherency, interrupts, >> etc) that >> I would not be completely confident to have validated by only testing this >> in qemu. >> >> Could you explain how you validated this (what kind of tests you did). >> >> I would be interested to know how the system behave in the following cases: >> - stopping cpu with guests pinned to specific cores >> - stopping a cpu with a guest pinned and only running on that one >> - checking with passthrough devices (for irq balancing) >> >> Then a general remark i have is that most of this code (if not all) is >> always in Xen >> even if CONFIG_CPU_HOTPLUG is not activated in xen config which will probably >> generate some dead code. Could we protect some of the code not used when >> HOTPLUG is not activated with if (is_enabled(CONFIG_CPU_HOTPLUG)) or >> equivalent forms ? >> >> Cheers >> Bertrand >> > > Hi Bertrand > > I’ve tested various pinning scenarios, and all of them work fine, as Xen > forcibly unpins everything that was pinned to the offlined CPU. > I’ve also explicitly checked that interrupts are getting moved to and > from cores when needed. > > I will update the next cover letter to explain testing better and also > try to test on some hardware to be sure.
Thanks. > > Can you please elaborate a little on what exactly you mean by “checking > with passthrough devices”? I suspect I am not fully getting the idea. If a guest has an hardware device assigned using passthrough and one of its core is removed, is the guest and hardware device continue to work well after ? Cheers Bertrand > > > -- > Mykyta
