[Xen-devel] vdso reported as anon in xenoprofile ?

["Amitabha Roy" <amitabha.roy@xxxxxxxxx>]

Hi

I'm trying to profile dbench on xen (unstable) using xenoprof and I
get reports which have a lot of references to anon, like this:


            86741 68.3065 dbench
             6098  4.8020 anon (tgid:7143 range:0xbfffe000-0xbffff000)
             4987  3.9271 anon (tgid:7138 range:0xbfffe000-0xbffff000)
             4630  3.6460 anon (tgid:7139 range:0xbfffe000-0xbffff000)
             4120  3.2444 anon (tgid:7140 range:0xbfffe000-0xbffff000)
             3846  3.0286 anon (tgid:7137 range:0xbfffe000-0xbffff000)
             3786  2.9814 anon (tgid:7142 range:0xbfffe000-0xbffff000)
             3554  2.7987 anon (tgid:7136 range:0xbfffe000-0xbffff000)
        

I know that range belongs to the vdso which implements signals and
system calls (so the kernel gets to choose between int 0x80 and
sysenter and other stuff).

My first question, more of a crib, is why is it reported as anon ? I
know that techincally it is userspace executable but is really mapped
in by the kernel. Is that why it is not attributed to either the
userspace binary or the kernel ? But there should at least be an
attribution to vdso there. It also does not help that there are no
symbols in that region (likely because the trampoline is declared as a
byte array of pure machine code).

My second question is more generic. Would anyone know why dbench is
spending so much time in that anon region ? It would seen to indicate
that it is spending a lot of time doing system calls (not executing
the call, just doing it !), or restarting them or getting signals.

Any pointers are welcome.


Thanks
-Amitabha

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