Re: [PATCH] perf/amd/ibs: add phy_addr_only software filter for ibs_op

[Huang Shijie <huangsj@hygon.cn>]

Hi Ravi,

> Can you please confirm if those additional samples are genuinely valid.

Yes.  
To answer this properly I re-ran the mysql test,
and verified the physical address of every captured sample against
the System RAM ranges in /proc/iomem.

Setup: 384-CPU Hygon box, v7.3-based kernel, MySQL 8 under sysbench
oltp_read_only, 400 threads.  Each round is a fresh 60s
sysbench run; after 15s of warmup, perf records ibs_op for 3s:

  $ perf record -e ibs_op/phy_addr_only=1/ -c 100000 --phys-data \
        -p <mysqld>                    # my patch
  $ perf record -e ibs_op// --phys-data --filter 'phys_addr != 0' \
        -c 100000 -p <mysqld>          # your suggestion

Rounds alternate p1 -> b1 -> p2 -> b2 -> p3 -> b3 so both methods see
the same load conditions.  Each record's phys_addr is then dumped with
"perf script -F pid,tid,phys_addr" and bisect-checked against the
System RAM ranges (read from /proc/iomem as root).

                     samples    phys_addr==0    non-zero in
    round  filter    captured   (valid=1,MSR=0)  System RAM
    -----  --------  ---------  ---------------  -----------
     p1    phy_only  15710042        0.10 %          98.61 %
     b1    bpf       14041851        0.00 %          98.55 %
     p2    phy_only  15580497        0.10 %          98.56 %
     b2    bpf       15416187        0.00 %          98.58 %
     p3    phy_only  15732582        0.10 %          98.59 %
     b3    bpf       15447397        0.00 %          98.58 %

Two observations:
1. The validity ratio is identical for both methods.  Of the non-zero
   addresses phy_addr_only delivers, 98.6 % fall inside System RAM --
   the same ratio the BPF-filtered set shows. 

2. The only set-level difference is 0.10 % of samples where
   dc_phy_addr_valid is set but IBSDCPHYSAD reads 0. 

Thanks,
Huang Shijie