ping... On Tue, 2016-06-14 at 17:54 +0800, Wei Jiangang wrote: > 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 > > >
