On 10/16/21 1:49 AM, Sebastian Andrzej Siewior wrote: > From: "Ahmed S. Darwish" <a.darwish@xxxxxxxxxxxxx> > > The Qdisc::running sequence counter has two uses: > > 1. Reliably reading qdisc's tc statistics while the qdisc is running > (a seqcount read/retry loop at gnet_stats_add_basic()). > > 2. As a flag, indicating whether the qdisc in question is running > (without any retry loops). > > For the first usage, the Qdisc::running sequence counter write section, > qdisc_run_begin() => qdisc_run_end(), covers a much wider area than what > is actually needed: the raw qdisc's bstats update. A u64_stats sync > point was thus introduced (in previous commits) inside the bstats > structure itself. A local u64_stats write section is then started and > stopped for the bstats updates. > > Use that u64_stats sync point mechanism for the bstats read/retry loop > at gnet_stats_add_basic(). > > For the second qdisc->running usage, a __QDISC_STATE_RUNNING bit flag, > accessed with atomic bitops, is sufficient. Using a bit flag instead of > a sequence counter at qdisc_run_begin/end() and qdisc_is_running() leads > to the SMP barriers implicitly added through raw_read_seqcount() and > write_seqcount_begin/end() getting removed. All call sites have been > surveyed though, and no required ordering was identified. > > Now that the qdisc->running sequence counter is no longer used, remove > it. > > Note, using u64_stats implies no sequence counter protection for 64-bit > architectures. This can lead to the qdisc tc statistics "packets" vs. > "bytes" values getting out of sync on rare occasions. The individual > values will still be valid. > > Signed-off-by: Ahmed S. Darwish <a.darwish@xxxxxxxxxxxxx> > Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx> I see this has been merged this week end before we could test this thing during work days :/ Just add a rate estimator on a qdisc: tc qd add dev lo root est 1sec 4sec pfifo then : [ 140.824352] ------------[ cut here ]------------ [ 140.824361] WARNING: CPU: 15 PID: 0 at net/core/gen_stats.c:157 gnet_stats_add_basic+0x97/0xc0 [ 140.824378] Modules linked in: ipvlan bonding vfat fat w1_therm i2c_mux_pca954x i2c_mux ds2482 wire cdc_acm ehci_pci ehci_hcd bnx2x mdio xt_TCPMSS ip6table_mangle ip6_tables ipv6 [ 140.824413] CPU: 15 PID: 0 Comm: swapper/15 Not tainted 5.15.0-smp-DEV #73 [ 140.824415] Hardware name: Intel RML,PCH/Ibis_QC_18, BIOS 2.48.0 10/02/2019 [ 140.824417] RIP: 0010:gnet_stats_add_basic+0x97/0xc0 [ 140.824420] Code: 2c 38 4a 03 5c 38 08 48 c7 c6 68 15 51 a4 e8 60 00 c7 ff 44 39 e0 72 db 89 d8 eb 05 31 c0 45 31 ed 4d 01 2e 49 01 46 08 eb 17 <0f> 0b 4d 85 ff 75 96 48 8b 02 48 8b 4a 08 49 01 06 89 c8 49 01 46 [ 140.824432] RSP: 0018:ffff99415fbc5e08 EFLAGS: 00010206 [ 140.824434] RAX: 0000000080000100 RBX: ffff9939812f41d0 RCX: 0000000000000001 [ 140.824436] RDX: ffff99399705e0b0 RSI: 0000000000000000 RDI: ffff99415fbc5e40 [ 140.824438] RBP: ffff99415fbc5e30 R08: 0000000000000000 R09: 0000000000000000 [ 140.824440] R10: 0000000000000000 R11: ffffffffffffffff R12: ffff99415fbd7740 [ 140.824441] R13: dead000000000122 R14: ffff99415fbc5e40 R15: 0000000000000000 [ 140.824443] FS: 0000000000000000(0000) GS:ffff99415fbc0000(0000) knlGS:0000000000000000 [ 140.824445] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 140.824447] CR2: 000000000087fff0 CR3: 0000000f11610006 CR4: 00000000000606e0 [ 140.824449] Call Trace: [ 140.824450] <IRQ> [ 140.824453] ? local_bh_enable+0x20/0x20 [ 140.824457] est_timer+0x5e/0x130 [ 140.824460] call_timer_fn+0x2c/0x110 [ 140.824464] expire_timers+0x4c/0xf0 [ 140.824467] __run_timers+0x16f/0x1b0 [ 140.824470] run_timer_softirq+0x1d/0x40 [ 140.824473] __do_softirq+0x142/0x2a1 [ 140.824477] irq_exit_rcu+0x6b/0xb0 [ 140.824480] sysvec_apic_timer_interrupt+0x79/0x90 [ 140.824483] </IRQ> [ 140.824493] asm_sysvec_apic_timer_interrupt+0x12/0x20 [ 140.824497] RIP: 0010:cpuidle_enter_state+0x19b/0x300 [ 140.824502] Code: ff 45 84 e4 74 20 48 c7 45 c8 00 00 00 00 9c 8f 45 c8 f7 45 c8 00 02 00 00 0f 85 e4 00 00 00 31 ff e8 c9 0d 88 ff fb 8b 45 bc <85> c0 78 52 48 89 de 89 c3 48 6b d3 68 48 8b 4c 16 48 4c 2b 6d b0 [ 140.824503] RSP: 0018:ffff99398089be60 EFLAGS: 00000246 [ 140.824505] RAX: 0000000000000004 RBX: ffffffffa446cb28 RCX: 000000000000001f [ 140.824506] RDX: 000000000000000f RSI: 0000000000000000 RDI: 0000000000000000 [ 140.824507] RBP: ffff99398089beb0 R08: 0000000000000002 R09: 00000020cf9326e4 [ 140.824508] R10: 0000000000638824 R11: 0000000000000000 R12: 0000000000000000 [ 140.824509] R13: 00000020c9c8d180 R14: ffffc4733fbe1c50 R15: 0000000000000004 [ 140.824511] cpuidle_enter+0x2e/0x40 [ 140.824514] do_idle+0x19f/0x240 [ 140.824517] cpu_startup_entry+0x25/0x30 [ 140.824519] start_secondary+0x7c/0x80 [ 140.824521] secondary_startup_64_no_verify+0xc3/0xcb [ 140.824525] ---[ end trace d64fa4b3dc94b292 ]---
