Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.
Hello,
after reading the available documentation in DRBD User-Guide
(http://www.drbd.org/users-guide/s-latency-tuning.html#s-latency-tuning-cpu-mask)
...
A mask of 12 (00001100) implies DRBD may use the third and fourth CPU.
...
and the man page drbd.conf:
...
The default value of cpu-mask is 0, which means that
DRBD's kernel threads should be spread over all CPUs of the machine.
This value must be given in hexadecimal notation.
...
I set the config parameter cpu-mask in drbd.conf to 255
(to enable usage of all 8 available cores) but got this:
# ps u 4387
USER PID %CPU %MEM VSZ RSS TTY STAT START TIME
COMMAND
root 4387 3.5 0.0 0 0 ? S 2010 1539:29
[drbd0_worker]
# taskset -c -p 4387
pid 4387's current affinity list: 0,2,4,6
But expected this list: 0,1,2,3,4,5,6,7
=> Conclusion:
1. The example in DRBD User-Guide is simply wrong
(drbd.conf: "cpu-mask 12;" => affinity list: 1,4)
2. The cpu-mask parameter has to be specified, as stated in the man
page,
as Hexstring ("cpu-mask ff;" to get the first 8 cpus) in drbd.conf
3. But if the parameter cpu-mask is explicit set to zero in drbd.conf
(to get it run on _all_ cpus) I get only the second cput (affinity
list: 1).
So in this aspect the man page is wrong about the default.
My DRBD Version is 8.3.9.
@linbit: Could this be fixed in User-Guide and man page
And I'm not sure, if it can safely fixed by setting the mask on running
[drbd1_worker], [drbd1_receiver] and [drbd1_asender] tasks like
this:
taskset -c -p 0-7 <drbdX_yyy pids>
(Because I won't like to shutdown drbd resources on primary)
Or may this triggers some race condition and drbd hangs or show other
erratic behaviour?
Kind Regards,
Roland
--
Roland.Friedwagner at wu.ac.at Phone: +43 1 31336 5377
IT Services - WU (Vienna University of Economics and Business)