On 04/05/21 14:22, Dongli Zhang wrote: > May I have if there is any feedback on this? To pr_err_once() here helps > narrow > down what is the root cause of cpu online failure. > > > The issue fixed by d7eb79c6290c ("KVM: kvmclock: Fix vCPUs > 64 can't be > online/hotpluged") is able to demonstrate how this pr_err_once() helps. > > Due to VM kernel issue, at most 64 VCPUs can online if host clocksource is > switched to hpet. > > # echo hpet > /sys/devices/system/clocksource/clocksource0/current_clocksource > > > By default, we have no idea why only 64 out of 100 VCPUs are online in VM. We > need to customize kernel to debug why some CPUs are not able to online. > > > We will have below and know the root cause is with kvmclock, if we add the > pr_err_once().
Isn't pr_debug() more appropriate here? Don't you want one on the cpuhp_down_callbacks() too? I *think* it's common now to have CONFIG_DYNAMIC_DEBUG enabled so one can enable that line when they need to https://www.kernel.org/doc/html/latest/admin-guide/dynamic-debug-howto.html I can see the appeal of pr_err_once() but I think this can fail for legitimate reasons and is not necessarily strictly always an error? Thanks -- Qais Yousef