Messages in this thread | | | From | Török Edwin <> | Subject | fix callgraphs of 32-bit processes on 64-bit kernels. | Date | Mon, 15 Mar 2010 17:34:19 +0200 |
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Hi,
Callgraph profiling 32-bit apps on a 64-bit kernel doesn't work. The reason is that perf_callchain_user tries to read a stackframe with 64-bit pointers, which is wrong for a 32-bit process.
This patch fixes that, and I am almost able to get nice callgraph profiles from 32-bit apps now! (except for some problems with perf itself when tracing kernel modules, see [1])
Page-faults can be traced nicely (sid-ia32 is a 32-bit chroot):
$ sudo perf record -e page-faults -f -g /home/edwin/sid-ia32/usr/bin/glxgears $ sudo perf report ... 45.33% libc-2.10.2.so [.] __GI_memcpy | --- __GI_memcpy _mesa_BufferDataARB _mesa_meta_Clear radeonUserClear r700Clear _mesa_Clear 0x8049367 0x804a6ba __libc_start_main 0x8049111
16.96% libc-2.10.2.so [.] __GI_memset | --- __GI_memset _tnl_init_vertices _swsetup_CreateContext r600CreateContext driCreateNewContext dri2CreateNewContext 0xf77ab7dd 0xf7783c67 0xf778514c 0x804974f 0x804a33d __libc_start_main 0x8049111
And CPU cycles can be traced too in userspace: $ sudo perf record -f -g /home/edwin/sid-ia32/usr/bin/glxgears $ sudo perf report --sort comm,dso [...] 44.97% glxgears r600_dri.so | |--5.85%-- r700SendSPIState | radeonEmitState | r700DrawPrims | | | |--95.45%-- vbo_save_playback_vertex_list | | execute_list | | _mesa_CallList | | neutral_CallList | | | | | |--38.10%-- 0x80494a8 | | | 0x804a6ba | | | __libc_start_main | | | 0x8049111 [....] 40.00% glxgears [kernel] | |--3.14%-- copy_user_generic_string | | | |--71.70%-- 0xffffffffa01b4493 | | 0xffffffffa01b7c0b | | 0xffffffffa018b45b | | 0xffffffffa00ca927 | | 0xffffffffa01c524e | | compat_sys_ioctl | | sysenter_dispatch | | 0xf77ca430 | | drmCommandWriteRead | | 0xf74d7ab5 | | 0xf74d89a4 | | rcommonFlushCmdBufLocked | | rcommonFlushCmdBuf | | radeonFlush | | _mesa_flush | | _mesa_Flush | | 0xf775f270 | | 0x804a6d5 | | __libc_start_main | | 0x8049111 | | | |--15.09%-- 0xffffffffa01c524e | | compat_sys_ioctl | | sysenter_dispatch | | 0xf77ca430 | | drmCommandWriteRead
[1] But there is a problem with the perf tool: it can't trace addresses in kernel modules. This is a problem regardless if the traced app is 32-bit or 64-bit; and regardless if I do callgraph profiling or not. See the above trace, where the kernel addresses have all ffffffffa0* without a symbol name.
If I look at /proc/kallsyms I can guess the symbols, for example 0xffffffffa01b4493 is probably this one: ffffffffa01b4411 t r600_cs_packet_parse [radeon]
If I record/report without callgraph its the same problem: [...] 24.01% glxgears [kernel] [k] 0xffffffffa01b4ee9 3.96% glxgears libdrm_radeon.so.1.0.0 [.] cs_gem_write_reloc 3.53% glxgears r600_dri.so [.] r700SendSPIState 2.77% glxgears r600_dri.so [.] r700DrawPrims 1.99% glxgears r600_dri.so [.] r700SendVSConsts
Kernel symbol for 0xffffffffa01b4ee9 is not shown, I can guess it is this one (hey it was an exact match!): ffffffffa01b4ee9 t r600_packet3_check [radeon]
It would be good if perf knew how to lookup symbols in kernel modules!
Best regards, --Edwin
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