Hi, When I trigger kernel crash and specify 'notsc' for capture-kernel, The process of kdump will be blocked at calibrate_delay_converge().
/* wait for "start of" clock tick */ ticks = jiffies; while (ticks == jiffies) ; /* nothing */ The reason is that the jiffies remains the same, no changed. serial console log as following, ............ [ 0.000000] Linux version 4.7.0-rc2+ (root@localhost.localdomain) (gcc version 4.8.2 20140120 (Red Hat 4.8.2-16) (GCC) ) #2 SMP Wed Jun 156 [ 0.000000] Kernel command line: BOOT_IMAGE=/vmlinuz-4.7.0-rc2+ root=/dev/mapper/centos-root ro rd.lvm.lv=centos/swap vconsole.font=latarcyrheb-sun16 rd.lvm.lv=centos/root crashkernel=256M vconsole.keymap=us console=tty0 console=ttyS0,115200n8 LANG=en_US.UTF-8 irqpoll nr_cpus=1 reset_devices cgroup_disable=memory mce=off numa=off panic=10 rootflags=nofail acpi_no_memhotplug notsc ............ [ 0.000000] tsc: Kernel compiled with CONFIG_X86_TSC, cannot disable TSC completely ............ [ 0.000000] clocksource: hpet: mask: 0xffffffff max_cycles: 0xffffffff, max_idle_ns: 133484882848 ns [ 0.000000] tsc: Fast TSC calibration using PIT [ 0.000000] tsc: Detected 3192.714 MHz processor [ 0.000000] Calibrating delay loop... # The last log is raised by calibrate_delay(), which calls calibrate_delay_converge() to compute the lpj value. # So far, I don't know why the jiffies stays the same. # But I found two methods can avoid this problem。 1)specify the 'lpj=<n>' with 'notsc' together. 2) revert the 70de9a9. commit 70de9a97049e0ba79dc040868564408d5ce697f9 Author: Alok Kataria <akata...@vmware.com> Date: Mon Nov 3 11:18:47 2008 -0800 x86: don't use tsc_khz to calculate lpj if notsc is passed Impact: fix udelay when "notsc" boot parameter is passed With notsc passed on commandline, tsc may not be used for udelays, make sure that we do not use tsc_khz to calculate the lpj value in such cases. IMO, The flow of getting tsc_khz as following, tsc_init()->x86_platform.calibrate_tsc()->native_calibrate_tsc()->quick_pit_calibrate(). No codes use or call 'rdtsc'. Even if ‘notsc’ is passed, the tsc_khz is credible. and we can get lpj by it. So I want to push a patch to revert the 70de9a9. Any comments or suggestions is appreciated. Thanks, wei