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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.
Data type profiling of the workload with cacheline info:
$ 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) ]
$ 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
$ 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)
Assisted-by: LLM
Reviewed-by: Namhyung Kim <namhyung@kernel.org>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
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