| Message ID | 20100318050513.GA6575@drongo (mailing list archive) |
|---|---|
| State | Not Applicable |
| Headers | show |
On Thu, Mar 18, 2010 at 04:05:13PM +1100, Paul Mackerras wrote: > This implements a powerpc version of perf_arch_fetch_caller_regs. > It's implemented in assembly because that way we can be sure there > isn't a stack frame for perf_arch_fetch_caller_regs. If it was in > C, gcc might or might not create a stack frame for it, which would > affect the number of levels we have to skip. > > With this, we see results from perf record -e lock:lock_acquire like > this: > > # Samples: 24878 > # > # Overhead Command Shared Object Symbol > # ........ .............. ................. ...... > # > 14.99% perf [kernel.kallsyms] [k] ._raw_spin_lock > | > --- ._raw_spin_lock > | > |--25.00%-- .alloc_fd > | (nil) > | | > | |--50.00%-- .anon_inode_getfd > | | .sys_perf_event_open > | | syscall_exit > | | syscall > | | create_counter > | | __cmd_record > | | run_builtin > | | main > | | 0xfd2e704 > | | 0xfd2e8c0 > | | (nil) > > ... etc. > > Signed-off-by: Paul Mackerras <paulus@samba.org> > Acked-by: Benjamin Herrenschmidt <benh@kernel.crashing.org> > --- > arch/powerpc/include/asm/asm-compat.h | 2 ++ > arch/powerpc/kernel/misc.S | 28 ++++++++++++++++++++++++++++ > 2 files changed, 30 insertions(+) > > diff --git a/arch/powerpc/include/asm/asm-compat.h b/arch/powerpc/include/asm/asm-compat.h > index c1b475a..a9b91ed 100644 > --- a/arch/powerpc/include/asm/asm-compat.h > +++ b/arch/powerpc/include/asm/asm-compat.h > @@ -28,6 +28,7 @@ > #define PPC_LLARX(t, a, b, eh) PPC_LDARX(t, a, b, eh) > #define PPC_STLCX stringify_in_c(stdcx.) > #define PPC_CNTLZL stringify_in_c(cntlzd) > +#define PPC_LR_STKOFF 16 > > /* Move to CR, single-entry optimized version. Only available > * on POWER4 and later. > @@ -51,6 +52,7 @@ > #define PPC_STLCX stringify_in_c(stwcx.) > #define PPC_CNTLZL stringify_in_c(cntlzw) > #define PPC_MTOCRF stringify_in_c(mtcrf) > +#define PPC_LR_STKOFF 4 > > #endif > > diff --git a/arch/powerpc/kernel/misc.S b/arch/powerpc/kernel/misc.S > index 2d29752..b485a87 100644 > --- a/arch/powerpc/kernel/misc.S > +++ b/arch/powerpc/kernel/misc.S > @@ -127,3 +127,31 @@ _GLOBAL(__setup_cpu_power7) > _GLOBAL(__restore_cpu_power7) > /* place holder */ > blr > + > +#ifdef CONFIG_EVENT_TRACING > +/* > + * Get a minimal set of registers for our caller's nth caller. > + * r3 = regs pointer, r5 = n. > + * > + * We only get R1 (stack pointer), NIP (next instruction pointer) > + * and LR (link register). These are all we can get in the > + * general case without doing complicated stack unwinding, but > + * fortunately they are enough to do a stack backtrace, which > + * is all we need them for. > + */ > +_GLOBAL(perf_arch_fetch_caller_regs) > + mr r6,r1 > + cmpwi r5,0 > + mflr r4 > + ble 2f > + mtctr r5 > +1: PPC_LL r6,0(r6) > + bdnz 1b > + PPC_LL r4,PPC_LR_STKOFF(r6) > +2: PPC_LL r7,0(r6) > + PPC_LL r7,PPC_LR_STKOFF(r7) > + PPC_STL r6,GPR1-STACK_FRAME_OVERHEAD(r3) > + PPC_STL r4,_NIP-STACK_FRAME_OVERHEAD(r3) > + PPC_STL r7,_LINK-STACK_FRAME_OVERHEAD(r3) > + blr > +#endif /* CONFIG_EVENT_TRACING */ Ingo has reported me that context-switches software events (not the trace event version) have crappy callchains. So, while looking into it: - PERF_COUNT_SW_CPU_MIGRATIONS provides no regs. Heh, and it event doesn't work because of this perf_swevent_add give up if regs are NULL. Has PERF_COUNT_SW_CPU_MIGRATIONS ever worked? - PERF_COUNT_SW_CONTEXT_SWITCHES uses task_pt_regs(). This seems a very wrong thing. We don't want the regs when a user task was interrupted or before a syscall. That notwithstanding task_pt_regs() on kernel threads has insane effects. What we want for both is a hot regs snapshot. I'm going to fix this. But it means the CONFIG_EVENT_TRACING dependency is not true anymore. So I can't keep the exported symbol of perf_arch_fetch_caller_regs() in trace_event_perf.c. The ideal would be to put the EXPORT_SYMBOL in perf_event.c but doing so in the same file a weak symbol is defined has unpredictable effects. So I'm going to make it a macro as I don't have the choice. I'll update ppc at the same time but I can't guarantee it will even build :) Thanks.
diff --git a/arch/powerpc/include/asm/asm-compat.h b/arch/powerpc/include/asm/asm-compat.h index c1b475a..a9b91ed 100644 --- a/arch/powerpc/include/asm/asm-compat.h +++ b/arch/powerpc/include/asm/asm-compat.h @@ -28,6 +28,7 @@ #define PPC_LLARX(t, a, b, eh) PPC_LDARX(t, a, b, eh) #define PPC_STLCX stringify_in_c(stdcx.) #define PPC_CNTLZL stringify_in_c(cntlzd) +#define PPC_LR_STKOFF 16 /* Move to CR, single-entry optimized version. Only available * on POWER4 and later. @@ -51,6 +52,7 @@ #define PPC_STLCX stringify_in_c(stwcx.) #define PPC_CNTLZL stringify_in_c(cntlzw) #define PPC_MTOCRF stringify_in_c(mtcrf) +#define PPC_LR_STKOFF 4 #endif diff --git a/arch/powerpc/kernel/misc.S b/arch/powerpc/kernel/misc.S index 2d29752..b485a87 100644 --- a/arch/powerpc/kernel/misc.S +++ b/arch/powerpc/kernel/misc.S @@ -127,3 +127,31 @@ _GLOBAL(__setup_cpu_power7) _GLOBAL(__restore_cpu_power7) /* place holder */ blr + +#ifdef CONFIG_EVENT_TRACING +/* + * Get a minimal set of registers for our caller's nth caller. + * r3 = regs pointer, r5 = n. + * + * We only get R1 (stack pointer), NIP (next instruction pointer) + * and LR (link register). These are all we can get in the + * general case without doing complicated stack unwinding, but + * fortunately they are enough to do a stack backtrace, which + * is all we need them for. + */ +_GLOBAL(perf_arch_fetch_caller_regs) + mr r6,r1 + cmpwi r5,0 + mflr r4 + ble 2f + mtctr r5 +1: PPC_LL r6,0(r6) + bdnz 1b + PPC_LL r4,PPC_LR_STKOFF(r6) +2: PPC_LL r7,0(r6) + PPC_LL r7,PPC_LR_STKOFF(r7) + PPC_STL r6,GPR1-STACK_FRAME_OVERHEAD(r3) + PPC_STL r4,_NIP-STACK_FRAME_OVERHEAD(r3) + PPC_STL r7,_LINK-STACK_FRAME_OVERHEAD(r3) + blr +#endif /* CONFIG_EVENT_TRACING */
This implements a powerpc version of perf_arch_fetch_caller_regs. It's implemented in assembly because that way we can be sure there isn't a stack frame for perf_arch_fetch_caller_regs. If it was in C, gcc might or might not create a stack frame for it, which would affect the number of levels we have to skip. With this, we see results from perf record -e lock:lock_acquire like this: # Samples: 24878 # # Overhead Command Shared Object Symbol # ........ .............. ................. ...... # 14.99% perf [kernel.kallsyms] [k] ._raw_spin_lock | --- ._raw_spin_lock | |--25.00%-- .alloc_fd | (nil) | | | |--50.00%-- .anon_inode_getfd | | .sys_perf_event_open | | syscall_exit | | syscall | | create_counter | | __cmd_record | | run_builtin | | main | | 0xfd2e704 | | 0xfd2e8c0 | | (nil) ... etc. Signed-off-by: Paul Mackerras <paulus@samba.org> Acked-by: Benjamin Herrenschmidt <benh@kernel.crashing.org> --- arch/powerpc/include/asm/asm-compat.h | 2 ++ arch/powerpc/kernel/misc.S | 28 ++++++++++++++++++++++++++++ 2 files changed, 30 insertions(+)