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SubjectRe: [PATCH] powerpc/perf_events: Implement perf_arch_fetch_caller_regs for powerpc
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> 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.

Should we put this comment in the code as well?

Mikey

> It's not ifdef'd
> because it is only 14 instructions long.
>
> 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>
> ---
> arch/powerpc/include/asm/asm-compat.h | 2 ++
> arch/powerpc/kernel/misc.S | 20 ++++++++++++++++++++
> 2 files changed, 22 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..4459500 100644
> --- a/arch/powerpc/kernel/misc.S
> +++ b/arch/powerpc/kernel/misc.S
> @@ -127,3 +127,23 @@ _GLOBAL(__setup_cpu_power7)
> _GLOBAL(__restore_cpu_power7)
> /* place holder */
> blr
> +
> +/*
> + * Get a minimal set of registers for our caller's nth caller.
> + * r3 = regs pointer, r5 = n.
> + */
> +_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
> _______________________________________________
> Linuxppc-dev mailing list
> Linuxppc-dev@lists.ozlabs.org
> https://lists.ozlabs.org/listinfo/linuxppc-dev
>


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