Re: zeros in frame pointer callchains

From: Namhyung Kim
Date: Tue Apr 12 2016 - 21:07:29 EST

Next message: green: "[PATCH 0/2] Couple of lustre cleanups"
Previous message: James Morris: "[GIT PULL] Keys bugfixes for 4.6"
In reply to: Arnaldo Carvalho de Melo: "zeros in frame pointer callchains"
Messages sorted by: [ date ] [ thread ] [ subject ] [ author ]

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] ([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] ([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] ([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] ([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])
> 8254.597 probe:vfs_getname:(ffffffff8124c06c) pathname="/etc/localtime")
> 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+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)

Next message: green: "[PATCH 0/2] Couple of lustre cleanups"
Previous message: James Morris: "[GIT PULL] Keys bugfixes for 4.6"
In reply to: Arnaldo Carvalho de Melo: "zeros in frame pointer callchains"
Messages sorted by: [ date ] [ thread ] [ subject ] [ author ]