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Message-ID: <CAADnVQ+N5UaBwLjtLGHAe1PCjpRzxxcFL45gbb0eHMDZD5+X6A@mail.gmail.com> Date: Thu, 5 Jun 2025 11:45:44 -0700 From: Alexei Starovoitov <alexei.starovoitov@...il.com> To: "Liang, Kan" <kan.liang@...ux.intel.com> Cc: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>, Namhyung Kim <namhyung@...nel.org>, Ian Rogers <irogers@...gle.com>, Mark Rutland <mark.rutland@....com>, LKML <linux-kernel@...r.kernel.org>, "linux-perf-use." <linux-perf-users@...r.kernel.org>, Stephane Eranian <eranian@...gle.com>, Chun-Tse Shao <ctshao@...gle.com>, Thomas Richter <tmricht@...ux.ibm.com>, Leo Yan <leo.yan@....com>, Aishwarya TCV <aishwarya.tcv@....com>, Venkat Rao Bagalkote <venkat88@...ux.ibm.com> Subject: Re: [PATCH V3] perf: Fix the throttle error of some clock events On Thu, Jun 5, 2025 at 6:46 AM Liang, Kan <kan.liang@...ux.intel.com> wrote: > > > > On 2025-06-04 7:21 p.m., Alexei Starovoitov wrote: > > On Wed, Jun 4, 2025 at 10:16 AM <kan.liang@...ux.intel.com> wrote: > >> > >> From: Kan Liang <kan.liang@...ux.intel.com> > >> > >> Both ARM and IBM CI reports RCU stall, which can be reproduced by the > >> below perf command. > >> perf record -a -e cpu-clock -- sleep 2 > >> > >> The issue is introduced by the generic throttle patch set, which > >> unconditionally invoke the event_stop() when throttle is triggered. > >> > >> The cpu-clock and task-clock are two special SW events, which rely on > >> the hrtimer. The throttle is invoked in the hrtimer handler. The > >> event_stop()->hrtimer_cancel() waits for the handler to finish, which is > >> a deadlock. Instead of invoking the stop(), the HRTIMER_NORESTART should > >> be used to stop the timer. > >> > >> There may be two ways to fix it. > >> - Introduce a PMU flag to track the case. Avoid the event_stop in > >> perf_event_throttle() if the flag is detected. > >> It has been implemented in the > >> https://lore.kernel.org/lkml/20250528175832.2999139-1-kan.liang@linux.intel.com/ > >> The new flag was thought to be an overkill for the issue. > >> - Add a check in the event_stop. Return immediately if the throttle is > >> invoked in the hrtimer handler. Rely on the existing HRTIMER_NORESTART > >> method to stop the timer. > >> > >> The latter is implemented here. > >> > >> Move event->hw.interrupts = MAX_INTERRUPTS before the stop(). It makes > >> the order the same as perf_event_unthrottle(). Except the patch, no one > >> checks the hw.interrupts in the stop(). There is no impact from the > >> order change. > >> > >> Reported-by: Leo Yan <leo.yan@....com> > >> Reported-by: Aishwarya TCV <aishwarya.tcv@....com> > >> Closes: https://lore.kernel.org/lkml/20250527161656.GJ2566836@e132581.arm.com/ > >> Reported-by: Alexei Starovoitov <alexei.starovoitov@...il.com> > >> Closes: https://lore.kernel.org/lkml/djxlh5fx326gcenwrr52ry3pk4wxmugu4jccdjysza7tlc5fef@ktp4rffawgcw/ > >> Reported-by: Venkat Rao Bagalkote <venkat88@...ux.ibm.com> > >> Closes: https://lore.kernel.org/lkml/8e8f51d8-af64-4d9e-934b-c0ee9f131293@linux.ibm.com/ > >> Signed-off-by: Kan Liang <kan.liang@...ux.intel.com> > > > > It seems the patch fixes one issue and introduces another ? > > > > Looks like the throttle event is sticky. > > Once it's reached the perf_event no longer works ? > > No. It should still work even the throttle is triggered. > > sdp@...4e6bce080:~$ sudo bash -c 'echo 10 > > /proc/sys/kernel/perf_event_max_sample_rate' > sdp@...4e6bce080:~$ sudo perf record -a -e cpu-clock -c10000 -- sleep 1 > [ perf record: Woken up 1 times to write data ] > [ perf record: Captured and wrote 0.559 MB perf.data (584 samples) ] With the patch applied above command hangs in my VM: # perf record -a -e cpu-clock -c10000 -- sleep 1 [ 43.656855] hrtimer: interrupt took 21640 ns [ 68.561052] watchdog: BUG: soft lockup - CPU#0 stuck for 41s! [perf:2253] [ 68.561056] Modules linked in: bpf_preload [ 68.561060] CPU: 0 UID: 0 PID: 2253 Comm: perf Not tainted 6.15.0-12294-gc89e5202e569 #1172 PREEMPT [ 68.561062] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.14.0-0-g155821a1990b-prebuilt.qemu.org 04/01/2014 [ 68.561063] RIP: 0010:handle_softirqs+0x77/0x2a0 [ 68.561070] Code: 6b 96 02 00 01 00 00 bd 0a 00 00 00 44 89 64 24 14 89 6c 24 10 40 88 7c 24 04 31 c0 65 66 89 05 5f 6b 96 02 fb bb ff ff ff ff <48> c7 c0 c0 f [ 68.561071] RSP: 0018:ffa0000000003fa0 EFLAGS: 00000246 [ 68.561072] RAX: 0000000000000000 RBX: 00000000ffffffff RCX: 00000000000006e0 [ 68.561073] RDX: 0000000000000007 RSI: ff1100010212e100 RDI: 0000000000000000 [ 68.561074] RBP: 000000000000000a R08: 0000000000000000 R09: 7fffffffffffffff [ 68.561074] R10: 00000005a3af2140 R11: 0000000000004601 R12: 0000000000400100 [ 68.561075] R13: 0000000000000000 R14: 0000000000000002 R15: 0000000000000000 [ 68.561111] FS: 00007fa1b536f780(0000) GS:ff110004abe26000(0000) knlGS:0000000000000000 [ 68.561112] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 68.561113] CR2: 0000000001c67a30 CR3: 000000010f2f3003 CR4: 00000000003716f0 [ 68.561113] Call Trace: [ 68.561170] <IRQ> [ 68.561174] irq_exit_rcu+0x91/0xb0 [ 68.561176] sysvec_apic_timer_interrupt+0x71/0x90 [ 68.561181] </IRQ> [ 68.561181] <TASK> [ 68.561182] asm_sysvec_apic_timer_interrupt+0x1a/0x20 [ 68.561184] RIP: 0010:generic_exec_single+0x33/0x120 [ 68.561188] Code: 65 39 3d 5c 4d 89 02 74 28 3b 3d b8 f5 17 02 0f 83 de 00 00 00 89 f8 48 0f a3 05 d8 f1 17 02 0f 83 ce 00 00 00 e8 bd fe ff ff <31> c0 5b 5d 9 [ 68.561189] RSP: 0018:ffa00000025a3cc0 EFLAGS: 00000206 [ 68.561190] RAX: 0000000000000000 RBX: ffffffff8145b310 RCX: ff110004abe26000 [ 68.561190] RDX: 0000000000000007 RSI: 0000000000000000 RDI: ff1100042fa26540 [ 68.561191] RBP: 0000000000000202 R08: 0000000000000000 R09: 0000000000000000 [ 68.561191] R10: ffa00000025a3ee0 R11: 0000000000000000 R12: ffa00000025a3d40 [ 68.561192] R13: ff11000100881220 R14: ff11000100880fc0 R15: 0000000000000000 [ 68.561192] ? sw_perf_event_destroy+0x70/0x70 [ 68.561197] smp_call_function_single+0xc4/0x110 [ 68.561199] ? sw_perf_event_destroy+0x70/0x70 [ 68.561200] event_function_call+0x160/0x170 [ 68.561202] ? ctx_resched+0x2d0/0x2d0 [ 68.561205] ? perf_event_set_state+0x60/0x60 [ 68.561206] ? _perf_event_disable+0x50/0x50 [ 68.561208] perf_event_for_each_child+0x37/0x80 [ 68.561209] ? _perf_event_disable+0x50/0x50 [ 68.561211] _perf_ioctl+0x1df/0xad0 [ 68.561213] ? __set_cpus_allowed_ptr+0x71/0x80 [ 68.561216] ? avc_has_perm+0x72/0x160 [ 68.561219] ? ldsem_down_write+0x1bb/0x1fc [ 68.561222] perf_ioctl+0x42/0x70 [ 68.561224] __x64_sys_ioctl+0x8f/0xd0 [ 68.561226] do_syscall_64+0x46/0x160 [ 68.561228] entry_SYSCALL_64_after_hwframe+0x4b/0x53 but only after a fresh boot. If I run bpf selftests before that it works. Like test_progs -t stacktrace_build_id_nmi followed by the same perf record -a -e cpu-clock .. it works fine.
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