Messages in this thread | | | Date | Thu, 30 Nov 2017 00:48:06 +0000 | From | Abderrahmane Benbachir <> | Subject | Re: Very Early boot time stamps support |
| |
Pavel Tatashin <pasha.tatashin@oracle.com> a écrit :
> Hi Abderrahmane, > >> I'm implementing a feature in ftrace to enable very early function tracing, >> I'm using tsc when x86_tsc feature is available, but it seems that you did >> similar work in your patch "[PATCH v9 0/6] Early boot time stamps for x86". >> >> I need to record timestamps at the start of start_kernel(), the first >> function to be traced is set_task_stack_end_magic. > > Early boot time stamps are available only after platforms are > initialized. This happens in: > > start_kernel() > setup_arch() > kvmclock_init() <-- right after this call. > > This was a request from Thomas, not to invent a new TSC calibration, > and instead rely on what is already available. This seems related to kvm/hypervisor, is there any available TSC calibration that could be used independently from kvm ?
> > So, while not covering the whole boot process, early boot clock is > still initialized pretty early. > > Here a few ideas how to make early boot clock to initialize earlier. > > 2. We could initialize TSC earlier only on those CPUs where hardware > tells us specifically TSC frequency i.e. cpuinfo(15) is available. See > native_calibrate_tsc() for an example. This is true for all the latest > Intel CPUs. Unfortunately, this does not work with qemu, as it returns > some garbage in cpuinfo(15), even when processor supports this feature > natively. Is this a bug in Qemu ?
| |