FW: is memory locking per core necessary?

Lange Norbert norbert.lange at andritz.com
Fri Jan 15 13:15:57 CET 2021


I originally had the Xenomai thread tied to another CPU-Core, hence the subject.
The issue happens also if all threads are tied to Core #0.

So the question should read: is memory locking per *thread* necessary?

> -----Original Message-----
> From: Lange Norbert
> Sent: Freitag, 15. Jänner 2021 13:14
> To: Xenomai (xenomai at xenomai.org) <xenomai at xenomai.org>
> Subject: is memory locking per core necessary?
>
> Hello,
>
> I am trying to track down some spurios relaxes.
>
> What happens is that I:
> -   cobalt_init calls  mlockall(MCL_CURRENT | MCL_FUTURE);
> -   allocate and initialize some data in the heap area
> -   spawn the xenomai-thread
> -   wait for notification from the xenomai-thread (so that I know, any
> initialization there is done)
> -   call mlockall(MCL_CURRENT | MCL_FUTURE) once more
> -   notify the xenomai-thread (only now the real work starts)
>
> Then the Xenomai thread will have spurios relaxes when writing data in the heap
> or bss (reads seem to be fine).
> I am a bit confused why this happens, adding a mlockall(MCL_CURRENT |
> MCL_FUTURE) in the Xenomai thread fixes the issue.
> Note that  the locking should happen even before spawning the threads.
>
> Message I get is:
> Jan 15 12:05:19 buildroot kernel: [Xenomai] switching realtime_packet to
> secondary mode after exception #14 from user-space at 0x40f3ed (pid 1383)
> Code is always a store to heap or bss.
>
> X86_64 + 4.19.152-cip37-xeno15-static + glibc 2.28
>
> /proc/pid/maps:
> 00429000-00435000 rw-p 00000000 00:00 0
> 014b5000-014f8000 rw-p 00000000 00:00 0                                  [heap]
>
> /proc/pid/smaps:
> 00429000-00435000 rw-p 00000000 00:00 0
> Size:                 48 kB
> KernelPageSize:        4 kB
> MMUPageSize:           4 kB
> Rss:                  48 kB
> Pss:                  48 kB
> Shared_Clean:          0 kB
> Shared_Dirty:          0 kB
> Private_Clean:         0 kB
> Private_Dirty:        48 kB
> Referenced:           48 kB
> Anonymous:            48 kB
> LazyFree:              0 kB
> AnonHugePages:         0 kB
> ShmemPmdMapped:        0 kB
> Shared_Hugetlb:        0 kB
> Private_Hugetlb:       0 kB
> Swap:                  0 kB
> SwapPss:               0 kB
> Locked:               48 kB
> THPeligible:    0
> VmFlags: rd wr mr mw me lo ac
> 014b5000-014f8000 rw-p 00000000 00:00 0                                  [heap]
> Size:                268 kB
> KernelPageSize:        4 kB
> MMUPageSize:           4 kB
> Rss:                 268 kB
> Pss:                 268 kB
> Shared_Clean:          0 kB
> Shared_Dirty:          0 kB
> Private_Clean:         0 kB
> Private_Dirty:       268 kB
> Referenced:          268 kB
> Anonymous:           268 kB
> LazyFree:              0 kB
> AnonHugePages:         0 kB
> ShmemPmdMapped:        0 kB
> Shared_Hugetlb:        0 kB
> Private_Hugetlb:       0 kB
> Swap:                  0 kB
> SwapPss:               0 kB
> Locked:              268 kB
> THPeligible:    0
> VmFlags: rd wr mr mw me lo ac
>
> Mit besten Grüßen / Kind regards
>
> NORBERT LANGE

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