Re: Cannot use address filtering with user register sampling

["Liang, Kan" <kan.liang@linux.intel.com>]

On 2022-08-24 8:14 p.m., Hongtao Yu wrote:
> Hi,
>  
> I was exploring address filtering together with user reg sampling on Intel Skylake hardware. The idea behind it is to make reg sampling more selectively. Unfortunately, I hit ` This CPU does not support address filtering` error. The command I ran is:
>  
>    perf record -e br_inst_retired.all_branches:uppp --user-regs=DI --filter 'filter * @/bin/ls'  ls
>  
>    This CPU does not support address filtering
>  
> IIUC, the br_inst_retired event is also hardware-based, similarly with the intel_pt event. But the latter works with address filtering while the former doesn’t. What is rational behind this?

The --filter only supports the tracepoint event(s) or or a hardware
trace, e.g., Intel PT. They trace and dump each single instruction. You
can use the --filter option to choose and only retrieve the
data/instructions you are interested.

Perf record -e br_inst_retired.all_branches event does sampling. I would
recommend you to use "-c" option to control the event period.(The number
of events that triggers a single sample.) For example, -c1000 means 1000
events occur then the HW dumps a sample (only for the 1000th event).
e.g.,
    perf record -e br_inst_retired.all_branches:uppp --user-regs=DI
-c1000 ls

Then you can use the post-processing tools, e.g., perf report or perf
script, to filter and output the results.
e.g.,
   perf script --dsos ls -F+uregs


Thanks,
Kan