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kernel_optimize_test/net/dccp
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Eric Dumazet a342cb4772 tcp: switch orphan_count to bare per-cpu counters 
[ Upstream commit 19757cebf0c5016a1f36f7fe9810a9f0b33c0832 ]

Use of percpu_counter structure to track count of orphaned
sockets is causing problems on modern hosts with 256 cpus
or more.

Stefan Bach reported a serious spinlock contention in real workloads,
that I was able to reproduce with a netfilter rule dropping
incoming FIN packets.

    53.56%  server  [kernel.kallsyms]      [k] queued_spin_lock_slowpath
            |
            ---queued_spin_lock_slowpath
               |
                --53.51%--_raw_spin_lock_irqsave
                          |
                           --53.51%--__percpu_counter_sum
                                     tcp_check_oom
                                     |
                                     |--39.03%--__tcp_close
                                     |          tcp_close
                                     |          inet_release
                                     |          inet6_release
                                     |          sock_close
                                     |          __fput
                                     |          ____fput
                                     |          task_work_run
                                     |          exit_to_usermode_loop
                                     |          do_syscall_64
                                     |          entry_SYSCALL_64_after_hwframe
                                     |          __GI___libc_close
                                     |
                                      --14.48%--tcp_out_of_resources
                                                tcp_write_timeout
                                                tcp_retransmit_timer
                                                tcp_write_timer_handler
                                                tcp_write_timer
                                                call_timer_fn
                                                expire_timers
                                                __run_timers
                                                run_timer_softirq
                                                __softirqentry_text_start

As explained in commit cf86a086a1 ("net/dst: use a smaller percpu_counter
batch for dst entries accounting"), default batch size is too big
for the default value of tcp_max_orphans (262144).

But even if we reduce batch sizes, there would still be cases
where the estimated count of orphans is beyond the limit,
and where tcp_too_many_orphans() has to call the expensive
percpu_counter_sum_positive().

One solution is to use plain per-cpu counters, and have
a timer to periodically refresh this cache.

Updating this cache every 100ms seems about right, tcp pressure
state is not radically changing over shorter periods.

percpu_counter was nice 15 years ago while hosts had less
than 16 cpus, not anymore by current standards.

v2: Fix the build issue for CONFIG_CRYPTO_DEV_CHELSIO_TLS=m,
    reported by kernel test robot <lkp@intel.com>
    Remove unused socket argument from tcp_too_many_orphans()

Fixes: dd24c00191 ("net: Use a percpu_counter for orphan_count")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: Stefan Bach <sfb@google.com>
Cc: Neal Cardwell <ncardwell@google.com>
Acked-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
2021-11-18 14:04:08 +01:00
..
ccids net: dccp: Convert to use the preferred fallthrough macro 2020-08-22 12:38:34 -07:00
ackvec.c net: dccp: delete repeated words 2020-08-24 17:31:20 -07:00
ackvec.h treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 500 2019-06-19 17:09:55 +02:00
ccid.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 500 2019-06-19 17:09:55 +02:00
ccid.h net: dccp: Replace zero-length array with flexible-array member 2020-02-28 12:08:37 -08:00
dccp.h tcp: switch orphan_count to bare per-cpu counters 2021-11-18 14:04:08 +01:00
diag.c inet_diag: Move the INET_DIAG_REQ_BYTECODE nlattr to cb->data 2020-02-27 18:50:19 -08:00
feat.c net: dccp: Convert to use the preferred fallthrough macro 2020-08-22 12:38:34 -07:00
feat.h treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 500 2019-06-19 17:09:55 +02:00
input.c net: dccp: Convert to use the preferred fallthrough macro 2020-08-22 12:38:34 -07:00
ipv4.c tcp: fix race condition when creating child sockets from syncookies 2020-11-23 16:32:33 -08:00
ipv6.c ipv6: weaken the v4mapped source check 2021-03-30 14:32:01 +02:00
ipv6.h treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 500 2019-06-19 17:09:55 +02:00
Kconfig dccp: Replace HTTP links with HTTPS ones 2020-07-13 11:54:07 -07:00
Makefile
minisocks.c dccp: don't duplicate ccid when cloning dccp sock 2021-09-22 12:27:56 +02:00
options.c net: dccp: Convert to use the preferred fallthrough macro 2020-08-22 12:38:34 -07:00
output.c net: dccp: Convert to use the preferred fallthrough macro 2020-08-22 12:38:34 -07:00
proto.c tcp: switch orphan_count to bare per-cpu counters 2021-11-18 14:04:08 +01:00
qpolicy.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 389 2019-06-05 17:37:11 +02:00
sysctl.c proc/sysctl: add shared variables for range check 2019-07-18 17:08:07 -07:00
timer.c inet: remove icsk_ack.blocked 2020-09-30 14:21:30 -07:00
trace.h