Re: [PATCH v4 1/3] powerpc/perf: Use stack siar instead of mfspr

[Nageswara Sastry <rnsastry@linux.ibm.com>]

On 18/08/21 10:45 pm, Kajol Jain wrote:
> Minor optimization in the 'perf_instruction_pointer' function code by
> making use of stack siar instead of mfspr.
> 
> Fixes: 75382aa72f06 ("powerpc/perf: Move code to select SIAR or pt_regs
> into perf_read_regs")
> Signed-off-by: Kajol Jain <kjain@linux.ibm.com>


Tested this patch series, not seeing any '0' values.
Tested-by: Nageswara R Sastry <rnsastry@linux.ibm.com>

example output:
# perf report -D | grep addr
0 26236879714 0x3dcc8 [0x38]: PERF_RECORD_SAMPLE(IP, 0x1): 1446/1446: 
0xc000000000113584 period: 1 addr: 0
0 26236882500 0x3dd00 [0x38]: PERF_RECORD_SAMPLE(IP, 0x1): 1446/1446: 
0xc000000000113584 period: 1 addr: 0
0 26236883436 0x3dd38 [0x38]: PERF_RECORD_SAMPLE(IP, 0x1): 1446/1446: 
0xc000000000113584 period: 10 addr: 0
...


> ---
>   arch/powerpc/perf/core-book3s.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/powerpc/perf/core-book3s.c b/arch/powerpc/perf/core-book3s.c
> index bb0ee716de91..1b464aad29c4 100644
> --- a/arch/powerpc/perf/core-book3s.c
> +++ b/arch/powerpc/perf/core-book3s.c
> @@ -2260,7 +2260,7 @@ unsigned long perf_instruction_pointer(struct pt_regs *regs)
>   		else
>   			return regs->nip;
>   	} else if (use_siar && siar_valid(regs))
> -		return mfspr(SPRN_SIAR) + perf_ip_adjust(regs);
> +		return siar + perf_ip_adjust(regs);
>   	else if (use_siar)
>   		return 0;		// no valid instruction pointer
>   	else
> 

-- 
Thanks and Regards
R.Nageswara Sastry