Hello all,
I am seeing significant differences in behaviour depending on whether I
spawn 2 Xenomai tasks from one program vs two programs. The 2 Xenomai
tasks that I spawn from the one program are line-for-line identical to
the 2 tasks that I spawn from two programs. The version where a single
mainline spawns 2 tasks produces the following output:
_*Single Mainline:*_
root@AKASRV:~$ dmesg | grep Xenomai
[Xenomai] scheduling class idle registered.
[Xenomai] scheduling class rt registered.
I-pipe: head domain Xenomai registered.
[Xenomai] allowing access to group 1100
[Xenomai] Cobalt v3.1 [DEBUG]
[Xenomai] switching Test1 to secondary mode after exception #1 from
user-space at 0x76ce932c (pid 313)
root@AKASRV:~$ cat /proc/xenomai/sched/stat
CPU PID MSW CSW XSC PF STAT %CPU NAME
0 0 0 82 0 0 00218000 99.7 [ROOT/0]
1 0 0 0 0 0 00218000 100.0 [ROOT/1]
0 311 43 47 139 0 002680c0 0.0
mutexOneFileTes
0 313 13 22 39 1 00248044 0.0 Test1
0 314 11 19 31 0 00248044 0.0 Test2
0 0 0 169036 0 0 00000000 0.3
[IRQ16: [timer]]
1 0 0 5458 0 0 00000000 0.0
[IRQ16: [timer]]
_*Two Mainlines:*_
The version where 2 mainlines each spawn 1 task each produces the
following output:
root@AKASRV:~$ dmesg | grep Xenomai
[Xenomai] scheduling class idle registered.
[Xenomai] scheduling class rt registered.
I-pipe: head domain Xenomai registered.
[Xenomai] allowing access to group 1100
[Xenomai] Cobalt v3.1 [DEBUG]
[Xenomai] switching mutexTest2 to secondary mode after exception #1 from
user-space at 0x76ec2d2e (pid 318)
[Xenomai] switching mutexTest2 to secondary mode after exception #1 from
user-space at 0x76eef642 (pid 318)
[Xenomai] switching mutexTest2 to secondary mode after exception #1 from
user-space at 0x76eee5aa (pid 318)
[Xenomai] switching mutexTest2 to secondary mode after exception #1 from
user-space at 0x76ec9eee (pid 318)
[Xenomai] switching Test2 to secondary mode after exception #1 from
user-space at 0x76eee5aa (pid 321)
root@AKASRV:~$ cat /proc/xenomai/sched/stat
CPU PID MSW CSW XSC PF STAT %CPU NAME
0 0 0 60 0 0 00218000 99.7 [ROOT/0]
1 0 0 45 0 0 00218000 100.0 [ROOT/1]
0 313 40 43 126 0 002680c0 0.0 mutexTest1
0 315 1 3 8 0 00240042 0.0
remote-agent
0 316 11 18 37 0 00248044 0.0 Test1
1 318 25 28 66 4 002680c0 0.0 mutexTest2
1 320 1 3 8 0 00240042 0.0
remote-agent
1 321 11 18 31 1 00248044 0.0 Test2
0 0 0 164476 0 0 00000000 0.3
[IRQ16: [timer]]
1 0 0 5324 0 0 00000000 0.0
[IRQ16: [timer]]
Does anyone have any ideas why the behaviour would be different if I
spawn the 2 tasks from 1 mainline vs 2 mainlines?
Also, any thoughts as to why a rt_mutex_bind() that causes a task switch
would apparently result in a page fault?
Some additional information:
* I do run the two mainline test case with the same Xenomai session by
using the --session=aka argument when they are started
* I do have Xenomai built with full debugging enabled so I can get
more debug information
* I am using Xenomai 3.1 with Linux kernel 4.19.144 on a Arm Cortex-A9
platform
* I got to these tests after chasing page faults for a few days. You
can see 1 page fault in Test1 in the stat output for the single
mainline case; I also see this page fault when using Linux to
capture page fault information after each Xenomai call. In the
single mainline case, the page fault occurs when the mutex that
Test2 is waiting for (rt_mutex_bind()) is created by Test1 causing a
task switch from Test1 to Test2.
* In the two mainline case, there are 4 page faults in the mainline
that spawns Test2 and then another page fault in Test2. Using the
Linux captures, I see that there are multiple page faults during
each rt_task_create() call - typically around 17 using Linux
captures. I have no idea why Xenomai stat reports 0 page faults in 2
of the 3 mainlines (mutexOneFileTest & mutexTest1) and 4 in the 3rd
mainline (mutexTest2). The Linux fault capture of task Test2 also
shows 1 page fault caused by the processing of the rt_mutex_bind()
where Test2 is waiting for Test1 to create the mutex (rt_mutex_create())
I've chased this problem for many days and am out of ideas to try. Any
suggestions would be gratefully appreciated.
Thanks
Peter
P.S. I am happy to post the C code if it is of use. I have 3 mainline C
files and 2 C files containing the Xenomai task code. The mainlines
#include the task C files so that I am guaranteed that the Xenomai tasks
are identical.
