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Date: Sat, 1 Oct 2022 17:16:08 +0000 From: Christophe Leroy <christophe.leroy@...roup.eu> To: Eric Dumazet <edumazet@...gle.com>, "netdev@...r.kernel.org" <netdev@...r.kernel.org>, David Dworken <ddworken@...gle.com>, Willem de Bruijn <willemb@...gle.com> CC: "David S. Miller" <davem@...emloft.net> Subject: 126 ms irqsoff Latency - Possibly due to commit 190cc82489f4 ("tcp: change source port randomizarion at connect() time") Hi, With recent kernels I have a huge irqsoff latency in my boards, shortly after startup, from the call to net_get_random_once() in __inet_hash_connect(). On a non instrumented kernel, IRQs are disabled during approximately 80 milliseconds. With the traces in goes to 126 milliseconds. Was apparently introduced by commit 190cc82489f4 ("tcp: change source port randomizarion at connect() time") Trace below. Would there be a way to perform the call to get_random_bytes() without disabling IRQ ? Thanks Christophe # tracer: irqsoff # # irqsoff latency trace v1.1.5 on 6.0.0-rc5-s3k-dev-02351-gebc95f69a7d4 # -------------------------------------------------------------------- # latency: 126337 us, #8207/8207, CPU#0 | (M:preempt VP:0, KP:0, SP:0 HP:0) # ----------------- # | task: CORSurv-352 (uid:0 nice:0 policy:0 rt_prio:0) # ----------------- # => started at: _raw_spin_lock_irqsave # => ended at: _raw_spin_unlock_irqrestore # # # _------=> CPU# # / _-----=> irqs-off/BH-disabled # | / _----=> need-resched # || / _---=> hardirq/softirq # ||| / _--=> preempt-depth # |||| / _-=> migrate-disable # ||||| / delay # cmd pid |||||| time | caller # \ / |||||| \ | / CORSurv-352 0d.... 4us : _raw_spin_lock_irqsave CORSurv-352 0d.... 13us+: preempt_count_add <-_raw_spin_lock_irqsave CORSurv-352 0d..1. 25us+: do_raw_spin_lock <-_raw_spin_lock_irqsave CORSurv-352 0d..1. 36us : get_random_bytes <-__inet_hash_connect CORSurv-352 0d..1. 45us : _get_random_bytes.part.0 <-__inet_hash_connect CORSurv-352 0d..1. 55us : crng_make_state <-_get_random_bytes.part.0 CORSurv-352 0d..1. 65us+: ktime_get_seconds <-crng_make_state CORSurv-352 0d..1. 77us+: crng_fast_key_erasure <-crng_make_state CORSurv-352 0d..1. 89us+: chacha_block_generic <-crng_fast_key_erasure CORSurv-352 0d..1. 101us+: chacha_permute <-chacha_block_generic CORSurv-352 0d..1. 129us : chacha_block_generic <-_get_random_bytes.part.0 CORSurv-352 0d..1. 139us+: chacha_permute <-chacha_block_generic CORSurv-352 0d..1. 160us : chacha_block_generic <-_get_random_bytes.part.0 CORSurv-352 0d..1. 170us+: chacha_permute <-chacha_block_generic CORSurv-352 0d..1. 191us : chacha_block_generic <-_get_random_bytes.part.0 CORSurv-352 0d..1. 200us+: chacha_permute <-chacha_block_generic CORSurv-352 0d..1. 221us : chacha_block_generic <-_get_random_bytes.part.0 CORSurv-352 0d..1. 231us+: chacha_permute <-chacha_block_generic 8182 x the above two line CORSurv-352 0d..1. 126275us : chacha_block_generic <-_get_random_bytes.part.0 CORSurv-352 0d..1. 126285us+: chacha_permute <-chacha_block_generic CORSurv-352 0d..1. 126309us : _raw_spin_unlock_irqrestore <-__do_once_done CORSurv-352 0d..1. 126318us+: do_raw_spin_unlock <-_raw_spin_unlock_irqrestore CORSurv-352 0d..1. 126330us+: _raw_spin_unlock_irqrestore CORSurv-352 0d..1. 126346us+: trace_hardirqs_on <-_raw_spin_unlock_irqrestore CORSurv-352 0d..1. 126387us : <stack trace> => tcp_v4_connect => __inet_stream_connect => inet_stream_connect => __sys_connect => system_call_exception => ret_from_syscall
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