Cant change kernel parameter dbc_max_pct

[Michel Helsdingen]

Hello,

This is my first post on this great forum. After being able to always find the answers I need I was not able to find a solution for my latest challenge.

One of our customers servers has a weird problem regarding a kernel parameter. First of when I start sam and enter the kernel module I immediately get the following warning:

After application of the parameter modification(s), one or more │ │
│───│ kernel parameters were found to violate their minimum or maximum │───│
│ │ allowable values. The values of these parameters have been adjusted │ │
│ │ as shown in the table below: │ │
│┌──│ │─┐ │
││ │ Parameter Old Value New Value │ ^ │
││ │ --------------------------------------------------------------- │ │
││ │ dbc_max_pct 0 2 │ │
││ │ dbc_min_pct 0 2 │ │
││ │ nswapdev 64 25

So as you can see SAM states there are 3 parameters that have a wrong value and that SAM wil adjust them. I want to have dbc_min_pct and dbc_max_pct at a value of 2. But when I go try and change the parameters to ANY value SAM will ouput:

│ The parameter modification(s) you have made have resulted in at least │ ││
││ │ one parameter evaluating to a value which is less than its minimum │ ││
││ │ allowable value. Parameter "dbc_min_pct", currently set to "0", has │ ││
││ │ evaluated to "0", which is less than its minimum allowable value of │ ││
││ │ "2". │

So in a nutshell, I am not able to change the parameter at all to any value. In SAM i see the current value is 2

[Robert-Jan Goossens]

Hoi Michel,

It is a bit difficult reading the above output, could you post the output from

# kmtune -q dbc_max_pct
# kmtune -q dbc_min_pct

Best regards,
Robert-Jan

[RAC_1]

Forget SAM. Do as follows from command line.

# cd /stand/build
# /usr/lbin/sysadm/system_prep -v -s system
# /usr/sbin/kmtune -s dbc_min_pct=2 -S ./system
The minimum value for dbc_min_pct is 2, and you can nor go bellow that.
# /usr/sbin/kmtune -s dbc_max_pct=2 -S ./system

Be forwarned that setting both values to 2, will result in static cache.
# /usr/sbin/kmtune -s nswapdev=10 -S ./system
# /usr/sbin/mk_kernel -s ./system
# mv /stand/system /stand/system.prev
# mv /stand/vmunix /stand/vmunix.prev
# mv ./system ../.
# /usr/sbin/kmupdate ./vmunix_test

# shutdown -ry 0

[Thierry Poels_1]

hi,

sorry I read this as "Current value = 0" and "New Value (modified by SAM) = 2".

Verify by checking "/stand/system", or by running "kmtune".

regards,
Thierry.

[Michel Helsdingen]

@Robert-Jan,

Thanks for your fast reply! Unfortuanatly kmtune is not available. I failed to mension that it envolves a HP 10.20 server which doesnt utilize kmtune as far as i can see? Or am I missing something?

@All

I see the rest of your answers also involve kmtune. I cant find that in the sbin or anywhere else. Please advise thnx!

[Robert-Jan Goossens]

Ok,

# strings /stand/system | grep dbc

Regards,
Robert-Jan

[Michel Helsdingen]

Hoi Robert,

Here is the output:

# strings /stand/system | grep dbc
dbc_max_pct 2
dbc_min_pct 2

Strangely enough it keeps telling me the value is 0. Even after a rebuild of the kernel and a reboot last week.

Thanks again

[Robert-Jan Goossens · Accepted solution]

So why does SAM thinks the dbc_min_pct is set to 0 ??

Parameter "dbc_min_pct", currently set to "0",

which kernel parameter did you change last week, do you still have an ols system file ?

[Robert-Jan Goossens]

by the way, could you check the settings inside your current kernel.

# strings /stand/vmunix | grep dbc

Robert-Jan

[Michel Helsdingen]

Hoi Robert Jan,

First of, here is the output:
# strings /stand/vmunix | grep dbc
dbc_max_pct
dbc_min_pct
dbc_bufpages
dbc_init
dbc_kdget
dbc_freemem
dbc_reference
dbc_alloc
dbc_hdr
dbc_ceiling
dbc_vhandcredit
dbc_parolemem
dbc_invalcount
dbc_steal_free_pages
rags_dbc_bufpages
dbc_nbuf
dbc_bio
dbc_stealavg
dbc_steal_factor
dbchan
dbchan2
dbc_max_pct 0
dbc_min_pct 0
smdt_odbcntl
lgdt_odbcntl

Secondly, the reason why we processed a new kernel last week was because we hoped that that would solve the problem last week since SAM stated that it would process a new kernel due to incorrect settings. But that didnt to it quite yet.

Any more thoughts?

[Robert-Jan Goossens]

Hoi Michel,

Could you compare my notes to the commands you made during the build of the new kernel.

10.X

1. Change directories to /stand/build.
# cd /stand/build

2. Create a new system file from the running kernel.
# /usr/lbin/sysadm/system_prep -s /stand/build/system

3. Edit the kernel with the planned changes.
# vi /stand/build/system

4. Build the new kernel.
# /usr/sbin/mk_kernel -s /stand/build/system

5. Move the old system and vmunix files so if anything goes wrong, the system
can be booted from the old kernel.
# mv /stand/system /stand/system.prev
# mv /stand/build/system /stand/system
# mv /stand/vmunix /stand/vmunix.prev
# mv /stand/build/vmunix_test /stand/vmunix

6. Reboot the system off the new kernel.
# shutdown -r -y now

Best regards,
Robert-Jan

[Michel Helsdingen]

Hoi Robert Jan!

It worked! The parameter now is correct! Thanks a bunch. U deserve 10 points but I cant change that anymore since I was to fast. Sorry for that.

Regards,
Michel

[Michel Helsdingen]

I was to fast. I was still able to give you 10 points :) Thanks again!