Re: [PATCH v6 5/5] perf test: Add false_sharing workload exhibiting cross-CPU false sharing

[Arnaldo Carvalho de Melo <acme@kernel.org>]

On Thu, Oct 01, 2026 at 12:28:13AM -0700, Namhyung Kim wrote:
> On Wed, Sep 30, 2026 at 11:37:16PM +0200, Arnaldo Carvalho de Melo wrote:
> > Add a 'perf test -w false_sharing' workload that hammers one shared
> > struct from several CPUs, shaped as a TCP connection: a read-mostly
> > identity (five-tuple) shares a cacheline with per-packet rx counters
> > (the false-sharing line), a second line has packet-path private tx and
> > congestion control counters, and a third the connection config.

> > The packet path runs in the main thread and up to four lookup threads
> > sum the five-tuple and pull the config, reading one volatile shared
> > instance directly so the accesses are PC-relative and resolvable by the
> > data type profiler.
> 
> It'd be great if you can share an output of data type profiling with
> cacheline info.  Probably like below?
> 
>   $ perf mem record -- perf test -w false_sharing
>  
>   $ perf report -s type,typecln -H --group --stdio

Sure, I should've added it there as I usually do :-\

Here it is, will add to the cset message as well:

root@x2:~# perf mem record -- perf test -r5 -w false_sharing
[ perf record: Woken up 19 times to write data ]
[ perf record: Captured and wrote 5.612 MB perf.data (72454 samples) ]
root@x2:~#
root@x2:~# perf report -s type,typecln -H --group --stdio
# Total Lost Samples: 0
#
# Samples: 72K of events 'cpu/mem-loads,ldlat=30/P, cpu/mem-stores/P'
# Event count (approx.): 1261814616
#
#            Overhead  Data Type / Data Type Cacheline
# ...................  ...............................
#
    88.99%  35.88%     struct net_conn
       56.43%  17.50%     struct net_conn: cache-line 0
       32.55%   0.00%     struct net_conn: cache-line 2
        0.01%  18.38%     struct net_conn: cache-line 1
    10.08%  63.03%     (unknown)
       10.08%  63.03%     (unknown): cache-line 0
     0.82%   0.13%     int
        0.82%   0.13%     int: cache-line 0
     0.01%   0.02%     struct folio
        0.01%   0.02%     struct folio: cache-line 0
     0.01%   0.03%     Elf64_Addr
        0.01%   0.03%     Elf64_Addr: cache-line 0
     0.01%   0.03%     struct sched_entity
        0.01%   0.03%     struct sched_entity: cache-line 1
        0.00%   0.00%     struct sched_entity: cache-line 4
        0.00%   0.00%     struct sched_entity: cache-line 2
        0.00%   0.00%     struct sched_entity: cache-line 3
        0.00%   0.00%     struct sched_entity: cache-line 0
     0.01%   0.00%     struct task_group
        0.01%   0.00%     struct task_group: cache-line 4
        0.00%   0.00%     struct task_group: cache-line 5
     0.00%   0.00%     struct css_rstat_cpu
        0.00%   0.00%     struct css_rstat_cpu: cache-line 0
root@x2:~#
root@x2:~# perf report -s type,typecln,typeoff -H --group --stdio
# Total Lost Samples: 0
#
# Samples: 72K of events 'cpu/mem-loads,ldlat=30/P, cpu/mem-stores/P'
# Event count (approx.): 1261814616
#
#               Overhead  Data Type / Data Type Cacheline / Data Type Offset
# ......................  ..................................................
#
    88.99%  35.88%        struct net_conn
       56.43%  17.50%        struct net_conn: cache-line 0
           9.81%   0.00%        struct net_conn +0xa (dport)
           9.54%   0.00%        struct net_conn +0x8 (sport)
           9.53%   0.00%        struct net_conn +0xc (state)
           9.48%   0.00%        struct net_conn +0xd (protocol)
           9.27%   0.00%        struct net_conn +0x4 (daddr)
           8.79%   0.00%        struct net_conn +0 (saddr)
           0.00%  12.08%        struct net_conn +0x10 (bytes_rx)
           0.00%   1.71%        struct net_conn +0x18 (packets_rx)
           0.00%   2.80%        struct net_conn +0x20 (rx_queue)
           0.00%   0.91%        struct net_conn +0x3c (last_ack)
       32.55%   0.00%        struct net_conn: cache-line 2
           5.70%   0.00%        struct net_conn +0x83 (rcv_wscale)
           5.46%   0.00%        struct net_conn +0x84 (keepalive_int)
           5.43%   0.00%        struct net_conn +0x82 (snd_wscale)
           5.39%   0.00%        struct net_conn +0x80 (mss)
           5.34%   0.00%        struct net_conn +0x88 (mark)
           5.23%   0.00%        struct net_conn +0x8c (priority)
        0.01%  18.38%        struct net_conn: cache-line 1
           0.01%   0.05%        struct net_conn +0x5c (retrans)
           0.00%   4.83%        struct net_conn +0x40 (bytes_tx)
           0.00%  10.63%        struct net_conn +0x48 (packets_tx)
           0.00%   1.54%        struct net_conn +0x58 (rtt_us)
           0.00%   1.07%        struct net_conn +0x50 (cwnd)
           0.00%   0.25%        struct net_conn +0x54 (ssthresh)
    10.08%  63.03%        (unknown)
       10.08%  63.03%        (unknown): cache-line 0
          10.08%  63.03%        (unknown)
     0.82%   0.13%        int      
        0.82%   0.13%        int: cache-line 0
           0.82%   0.13%        int +0 (no field)
     0.01%   0.02%        struct folio
        0.01%   0.02%        struct folio: cache-line 0
           0.01%   0.00%        struct folio +0 (flags.f)
           0.00%   0.01%        struct folio +0x34 (_refcount.counter)
           0.00%   0.00%        struct folio +0x18 (mapping)
: