On 18-06-29 09:30:10, Thomas Gleixner wrote: > On Thu, 28 Jun 2018, Pavel Tatashin wrote: > > On Thu, Jun 28, 2018 at 11:23 AM Thomas Gleixner <tglx@xxxxxxxxxxxxx> wrote: > > Hi Thomas, > > > > In addition to above, we have xen hvm: > > > > setup_arch() > > ... > > init_hypervisor_platform(); > > x86_init.hyper.init_platform(); > > xen_hvm_guest_init() > > xen_hvm_init_time_ops(); > > Duh. Missed that completely. > > > ... > > tsc_early_delay_calibrate(); > > tsc_khz = x86_platform.calibrate_tsc(); == xen_tsc_khz() > > ... > > > > Which works early. > > > > So, what should we do with xen, which seems to be the only platform > > that would provide different tsc frequency early and late, because of > > different calibration method? > > Fix it? I have no idea why XEN has two variants of the scheme and I neither > have a clue why the KVM clock stuff is late. kvm clock I have fixed in my series. http://lkml.kernel.org/r/20180621212518.19914-5-pasha.tatashin@xxxxxxxxxx It was late because, it depended on memblock, which is initialized later, after e820 ranges are read. So, after my series kvm clock will work right after init_hypervisor_platform, the same as with most other hypervisors. With xen, it is a little more challenging: I do not have a hardware configured to run xen to test it. On the other hand, most likely that tsc_early_delay_calibrate() now fails to calibrate tsc on xen, and calibrates correctly later in tsc_init(). I doubt, that we can use CPUID method to determine tsc frequency on xen cpu. Anyways, that would be accidental behavior. To make xen clock available early, we need HYPERVISOR_shared_info. So, at least that part of xen_setup_shared_info() must be called/available from init_hypervisor_platform(): void xen_setup_shared_info(void) { set_fixmap(FIX_PARAVIRT_BOOTMAP, xen_start_info->shared_info); HYPERVISOR_shared_info = (struct shared_info *)fix_to_virt(FIX_PARAVIRT_BOOTMAP); xen_setup_mfn_list_list(); ... Which, I have no idea if it is possible, or safe to do. For now, in my series, I would like check in tsc_early_init() if we are running xen, and set tsc_khz to 0 if so. Later in tsc_init() we will get a proper calibration. The question is how to make this check least intrusive. Pavel -- To unsubscribe from this list: send the line "unsubscribe linux-s390" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
