Re: [PATCH] powerpc/perf/hv-gpci: Fix the logic to compute counter value from the hcall result buffer.

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

On 13/08/21 1:51 pm, Kajol Jain wrote:
> H_GetPerformanceCounterInfo (0xF080) hcall returns the counter data in the
> result buffer. Result buffer has specific format defined in the PAPR
> specification. One of the field is counter offset and width of the counter
> data returned.
> 
> Counter data are returned in a unsigned char array. To
> get the final counter data, these values should be left shifted
> byte at a time. But commit 220a0c609ad17 ("powerpc/perf: Add support
> for the hv gpci (get performance counter info) interface") made the
> shifting bitwise. Because of this, hcall counters values could end up
> in lower side, which messes the counter prev vs now calculation. This
> lead to huge counter value reporting
> 
> [command]#: perf stat -e hv_gpci/system_tlbie_count_and_time_tlbie_instructions_issued/
>             -C 0 -I 1000
>          time             counts unit events
>       1.000078854 18,446,744,073,709,535,232      hv_gpci/system_tlbie_count_and_time_tlbie_instructions_issued/
>       2.000213293                  0      hv_gpci/system_tlbie_count_and_time_tlbie_instructions_issued/
>       3.000320107                  0      hv_gpci/system_tlbie_count_and_time_tlbie_instructions_issued/
>       4.000428392                  0      hv_gpci/system_tlbie_count_and_time_tlbie_instructions_issued/
>       5.000537864                  0      hv_gpci/system_tlbie_count_and_time_tlbie_instructions_issued/
>       6.000649087                  0      hv_gpci/system_tlbie_count_and_time_tlbie_instructions_issued/
>       7.000760312                  0      hv_gpci/system_tlbie_count_and_time_tlbie_instructions_issued/
>       8.000865218             16,448      hv_gpci/system_tlbie_count_and_time_tlbie_instructions_issued/
>       9.000978985 18,446,744,073,709,535,232      hv_gpci/system_tlbie_count_and_time_tlbie_instructions_issued/
>      10.001088891             16,384      hv_gpci/system_tlbie_count_and_time_tlbie_instructions_issued/
>      11.001201435                  0      hv_gpci/system_tlbie_count_and_time_tlbie_instructions_issued/
>      12.001307937 18,446,744,073,709,535,232      hv_gpci/system_tlbie_count_and_time_tlbie_instructions_issued/
> 
> Patch here fixes the shifting logic to make is byte-wise with which no more the issue seen.
> 
> Fixes: e4f226b1580b3 ("powerpc/perf/hv-gpci: Increase request buffer size")
> Reported-by: Nageswara R Sastry<rnsastry@linux.ibm.com>
> Signed-off-by: Kajol Jain <kjain@linux.ibm.com>

Tested-by: Nageswara R Sastry<rnsastry@linux.ibm.com>

Now not seeing huge numbers.

# perf stat -e 
hv_gpci/system_tlbie_count_and_time_tlbie_instructions_issued/ -C 0 -I 1000
#           time             counts unit events
      1.001023931             26,624 
hv_gpci/system_tlbie_count_and_time_tlbie_instructions_issued/
      2.002176767                  0 
hv_gpci/system_tlbie_count_and_time_tlbie_instructions_issued/
      3.003296382                  0 
hv_gpci/system_tlbie_count_and_time_tlbie_instructions_issued/
      4.004385311             33,280 
hv_gpci/system_tlbie_count_and_time_tlbie_instructions_issued/


> ---
>   arch/powerpc/perf/hv-gpci.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/powerpc/perf/hv-gpci.c b/arch/powerpc/perf/hv-gpci.c
> index d48413e28c39..c756228a081f 100644
> --- a/arch/powerpc/perf/hv-gpci.c
> +++ b/arch/powerpc/perf/hv-gpci.c
> @@ -175,7 +175,7 @@ static unsigned long single_gpci_request(u32 req, u32 starting_index,
>   	 */
>   	count = 0;
>   	for (i = offset; i < offset + length; i++)
> -		count |= arg->bytes[i] << (i - offset);
> +		count |= (u64)(arg->bytes[i]) << ((length - 1 - (i - offset)) * 8);
>   
>   	*value = count;
>   out:
> 

-- 
Thanks and Regards
R.Nageswara Sastry