According to this discussion: http://lkml.org/lkml/2008/7/25/338 http://lkml.org/lkml/2008/7/26/72
Frame pointers do nothing useful on PowerPC, so lib/Kconfig.debug makes CONFIG_FRAME_POINTER unselectable on PPC targets. But ftrace.h requires CONFIG_FRAME_POINTER for CALLER_ADDR macros. Therefore tracing is completely useless on PowerPC: [...] <idle>-0 0X.h3 2us+: 0:140:R + [000] 1733:120:S mvtsd <idle>-0 0X.h3 9us+: 0 (0) <idle>-0 0X..3 72us : 0 (0) <idle>-0 0X..3 73us : 0:140:R ==> [000] 1733:120:R mvtsd On PPC we can safely use __builtin_return_address(1..6) w/o frame pointers, and with this patch the trace output looks OK: [...] <idle>-0 0X.h3 2us+: 0:140:R + [000] 1740:120:S mvtsd <idle>-0 0X.h3 9us+: hrtimer_wakeup (__run_hrtimer) <idle>-0 0X..3 87us : cpu_idle (__got2_end) <idle>-0 0X..3 89us : 0:140:R ==> [000] 1740:120:R mvtsd Signed-off-by: Anton Vorontsov <avoront...@ru.mvista.com> --- Btw, on PowerPC tracing is also broken w/o "ring-buffer: fix alignment problem" patch (currently collecting dust in the -tip tree, commit 082605de5f82eb692cc90f7fda071cc01bb5ac34). Any chance the fix go into Linus' tree, to not waste other people's time bisecting and debugging the problem? ;-) For google: tracing, regression, "ring-buffer: move some metadata into buffer page", commit abc9b56d66fbd4d93302ef4bf6fa726e1b8255f9, answer is here. include/linux/ftrace.h | 2 +- 1 files changed, 1 insertions(+), 1 deletions(-) diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h index 9c5bc6b..13eba02 100644 --- a/include/linux/ftrace.h +++ b/include/linux/ftrace.h @@ -146,7 +146,7 @@ static inline void __ftrace_enabled_restore(int enabled) #endif } -#ifdef CONFIG_FRAME_POINTER +#if defined(CONFIG_FRAME_POINTER) || defined(CONFIG_PPC) /* TODO: need to fix this for ARM */ # define CALLER_ADDR0 ((unsigned long)__builtin_return_address(0)) # define CALLER_ADDR1 ((unsigned long)__builtin_return_address(1)) -- 1.5.6.5 _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@ozlabs.org https://ozlabs.org/mailman/listinfo/linuxppc-dev
