Re: [Crash-utility] [PATCH] Fix machdep->HZ calculation for kernel versions > 2.6.0
在 2021年01月12日 16:24, HAGIO KAZUHITO(萩尾 一仁) 写道:
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?
The symbol 'cfq_slice_async' has been removed from upstream kernel:
f382fb0bcef4 ("block: remove legacy IO schedulers")
And RHEL8 also removed it.
We should search for an alternate way like the current one first.
Currently, there are several ways to get the value of HZ as below:
[1] calculate hz via the symbol 'cfq_slice_async'
But this symbol has been removed from upstream kernel
[2] hardcode hz with the value 1000 (if kernel version > 2.6.0)
[3] get the hz value from vmcore, but that relies on kernel config
such as CONFIG_IKCONFIG, etc.
[4] Use sysconf(_SC_CLK_TCK) on some arches, not all arches.
See the micro definition of HZ in the defs.h
There seems to be no perfect solution. Any ideas?
Thanks.
Lianbo
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@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.
>