[Crash-utility] [PATCH] Fix machdep->HZ calculation for kernel versions > 2.6.0

[HAGIO KAZUHITO(萩尾 一仁)]

Hi Bhupesh,

-----Original Message-----
> We have hard-coded the HZ value for some ARCHs to either 1000 or 100
> (mainly for kernel versions > 2.6.0), which causes 'help -m' to show
> an incorrect hz value for various architectures.

Good catch.  but seems crash uses (cfq_slice_async * 25) for machdep->hz
if it exists (please see task_init()), RHEL7 has it, but RHEL8 does not.
What do you see on RHEL8 for x86_64 with your patch?

We should search for an alternate way like the current one first.

Thanks,
Kazu

> 
> I tested this on ppc64le and x86_64 and the hz value reported is 1000,
> whereas the kernel CONFIG_HZ_100 is set to Y. See some logs below:
> 
> crash> help -m
>               flags: 124000f5
> (KSYMS_START|MACHDEP_BT_TEXT|VM_4_LEVEL|VMEMMAP|VMEMMAP_AWARE|PHYS_ENTRY_L4|SWAP_ENTRY_L4|RADIX_MMU|OP
> AL_FW)
>              kvbase: c000000000000000
>   identity_map_base: c000000000000000
>            pagesize: 65536
>           pageshift: 16
>            pagemask: ffffffffffff0000
>          pageoffset: ffff
>           stacksize: 16384
>                  hz: 1000
>                 mhz: 2800
> 
> [host at rhel7]$ grep CONFIG_HZ_100= redhat/configs/kernel-3.10.0-ppc64le.config
> CONFIG_HZ_100=y
> 
> Fix the same by using the sysconf(_SC_CLK_TCK) value instead of the
> hardcoded HZ values depending on kernel versions.
>