Messages in this thread | | | Date | Wed, 13 Apr 2016 10:06:57 +0900 | From | Namhyung Kim <> | Subject | Re: zeros in frame pointer callchains |
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Hi Arnaldo,
On Tue, Apr 12, 2016 at 10:38:47AM -0300, Arnaldo Carvalho de Melo wrote: > Hi, > > Namhyung, while working on supporting callchains in 'perf trace' I > noticed something I think we discussed at some point, zeros in frame pointer > callchains... > > Oh well figured it out, its probably userspace not having frame > pointers, grrr anyway, keeping the rest of the message, for reference, > but now I think we need to have some expressiveness to say that for that > particular event we want to use perf_event_attr.exclude_callchain_user... > > First add a special probe point that 'perf trace' uses, if present: > > # perf probe 'vfs_getname=getname_flags:72 pathname=filename:string' > > Then lets ask to see just when this thing hits, no syscall > printing whatsoever ('trace' == 'perf trace'), sometimes just a few > zeros at the top, sometimes a long series, need to investigate how to > chop those off in the kernel, not to use the ring buffer needlessly, > will start chopping these in userspace (in perf trace):
My solution was to look at /proc/sys/vm/mmap_min_addr [1]. For kernel it'd be simply discarding callchains after seeing an address below the mmap_min_addr. For userspace, it requires to carry the mmap_min_addr via feature bit or something. Or Maybe we can just discard addresses under 4096 for simplicity?
[1] https://lkml.org/lkml/2015/11/26/40
Thanks, Namhyung
> > # trace --no-sys --ev probe:vfs_getname/call-graph=fp/ > > 34033.533 probe:vfs_getname:(ffffffff8124c06c) pathname="/usr/share/pixmaps") > getname_flags+0xfe20009d ([kernel.kallsyms]) > user_path_at_empty+0xfe200023 ([kernel.kallsyms]) > vfs_fstatat+0xfe200066 ([kernel.kallsyms]) > SYSC_newstat+0xfe20002e ([kernel.kallsyms]) > sys_newstat+0xfe20000e ([kernel.kallsyms]) > entry_SYSCALL_64_fastpath+0xfe20001a ([kernel.kallsyms]) > __xstat64+0xffff011e90b98015 (/usr/lib64/libc-2.22.so) > [0] ([unknown]) > [0] ([unknown]) > [0] ([unknown]) > [0] ([unknown]) > 36001.681 probe:vfs_getname:(ffffffff8124c06c) pathname="/var/tmp") > getname_flags+0xfe20009d ([kernel.kallsyms]) > user_path_at_empty+0xfe200023 ([kernel.kallsyms]) > vfs_fstatat+0xfe200066 ([kernel.kallsyms]) > SYSC_newstat+0xfe20002e ([kernel.kallsyms]) > sys_newstat+0xfe20000e ([kernel.kallsyms]) > entry_SYSCALL_64_fastpath+0xfe20001a ([kernel.kallsyms]) > __xstat64+0xffff00b816a28015 (/usr/lib64/libc-2.22.so) > [0] ([unknown]) > [0] ([unknown]) > [0] ([unknown]) > [0] ([unknown]) > [0] ([unknown]) > [0] ([unknown]) > [0] ([unknown]) > [0] ([unknown]) > [0] ([unknown]) > [0] ([unknown]) > [0] ([unknown]) > [0] ([unknown]) > [0] ([unknown]) > [0] ([unknown]) > [0] ([unknown]) > [0] ([unknown]) > [0] ([unknown]) > [0] ([unknown]) > [0] ([unknown]) > [0] ([unknown]) > [0] ([unknown]) > [0] ([unknown]) > [0] ([unknown]) > [0] ([unknown]) > [0] ([unknown]) > [0] ([unknown]) > [0] ([unknown]) > [0] ([unknown]) > [0] ([unknown]) > [0] ([unknown]) > [0] ([unknown]) > [0] ([unknown]) > [0] ([unknown]) > [0] ([unknown]) > [0] ([unknown]) > [0] ([unknown]) > [0] ([unknown]) > [0] ([unknown]) > [0] ([unknown]) > [0] ([unknown]) > [0] ([unknown]) > [0] ([unknown]) > [0] ([unknown]) > [0] ([unknown]) > [0] ([unknown]) > [0] ([unknown]) > [0] ([unknown]) > [0] ([unknown]) > [0] ([unknown]) > [0] ([unknown]) > [0] ([unknown]) > [0] ([unknown]) > [0] ([unknown]) > [0] ([unknown]) > [0] ([unknown]) > [0] 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([unknown]) > [0] ([unknown]) > [0] ([unknown]) > [0] ([unknown]) > [0] ([unknown]) > [0] ([unknown]) > [0] ([unknown]) > [0] ([unknown]) > 36001.696 probe:vfs_getname:(ffffffff8124c06c) pathname="/var/tmp") > getname_flags+0xfe20009d ([kernel.kallsyms]) > user_path_at_empty+0xfe200023 ([kernel.kallsyms]) > sys_access+0xfe2000b4 ([kernel.kallsyms]) > entry_SYSCALL_64_fastpath+0xfe20001a ([kernel.kallsyms]) > __GI___access+0xffff00b816a28007 (/usr/lib64/libc-2.22.so) > [0] ([unknown]) > [0] ([unknown]) > [0] ([unknown]) > [0] ([unknown]) > [0] ([unknown]) > [0] ([unknown]) > [0] ([unknown]) > [0] ([unknown]) > [0] ([unknown]) > [0] ([unknown]) > [0] ([unknown]) > [0] ([unknown]) > [0] ([unknown]) > [0] ([unknown]) > [0] ([unknown]) > [0] ([unknown]) > [0] ([unknown]) > [0] ([unknown]) > [0] ([unknown]) > [0] ([unknown]) > [0] ([unknown]) > [0] ([unknown]) > [0] ([unknown]) > [0] ([unknown]) > [0] ([unknown]) > [0] ([unknown]) > [0] ([unknown]) > [0] ([unknown]) > [0] ([unknown]) > [0] 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([kernel.kallsyms]) > __xstat64+0xffff0104f5696015 (/usr/lib64/libc-2.22.so) > [0] ([unknown]) > [0] ([unknown]) > 9001.567 probe:vfs_getname:(ffffffff8124c06c) pathname="/etc/firewalld/ipsets") > getname_flags+0xfe20009d ([kernel.kallsyms]) > user_path_at_empty+0xfe200023 ([kernel.kallsyms]) > sys_inotify_add_watch+0xfe200098 ([kernel.kallsyms]) > entry_SYSCALL_64_fastpath+0xfe20001a ([kernel.kallsyms]) > inotify_add_watch+0xffff008bb9432007 (/usr/lib64/libc-2.22.so) > 9450.181 probe:vfs_getname:(ffffffff8124c06c) pathname="/root") > getname_flags+0xfe20009d ([kernel.kallsyms]) > user_path_at_empty+0xfe200023 ([kernel.kallsyms]) > sys_inotify_add_watch+0xfe200098 ([kernel.kallsyms]) > entry_SYSCALL_64_fastpath+0xfe20001a ([kernel.kallsyms]) > inotify_add_watch+0xffff01b7aa4f2007 (/usr/lib64/libc-2.22.so)
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