linux-kernel - Re: Unexplained long boot delays [Was Re: [GIT PULL] RCU changes for v6.9]

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Message-ID: <87sf0sldbi.ffs@tglx>
Date: Thu, 14 Mar 2024 22:21:21 +0100
From: Thomas Gleixner <tglx@...utronix.de>
To: Florian Fainelli <f.fainelli@...il.com>, Boqun Feng <boqun.feng@...il.com>
Cc: Frederic Weisbecker <frederic@...nel.org>, "Russell King (Oracle)"
 <linux@...linux.org.uk>, Joel Fernandes <joel@...lfernandes.org>,
 Anna-Maria Behnsen <anna-maria@...utronix.de>, Linus Torvalds
 <torvalds@...ux-foundation.org>, linux-kernel@...r.kernel.org,
 kernel-team@...a.com, paulmck@...nel.org, mingo@...nel.org,
 rcu@...r.kernel.org, neeraj.upadhyay@....com, urezki@...il.com,
 qiang.zhang1211@...il.com, bigeasy@...utronix.de, chenzhongjin@...wei.com,
 yangjihong1@...wei.com, rostedt@...dmis.org, Justin Chen
 <justin.chen@...adcom.com>
Subject: Re: Unexplained long boot delays [Was Re: [GIT PULL] RCU changes
 for v6.9]

On Thu, Mar 14 2024 at 21:45, Thomas Gleixner wrote:
> On Thu, Mar 14 2024 at 12:09, Florian Fainelli wrote:
>> https://gist.github.com/ffainelli/cb562c1a60ef8e0e69e7d42143c48e8f
>>
>> this one is does include the tmigr events. Thanks!
>
> You need 8ca1836769d758e4fbf5851bb81e181c52193f5d too.

So from the above trace it's clear where it goes south:

[  236.318158]   <idle>-0         3..s.. 2928466us : tmigr_handle_remote: group=aecb05cb lvl=0
[  236.326526]   <idle>-0         3d.s.. 2928467us : tmigr_handle_remote_cpu: cpu=0 parent=aecb05cb wakeup=9223372036854775807
[  236.357809]   <idle>-0         3d.s.. 2928469us : tmigr_update_events: child=00000000 group=aecb05cb group_lvl=0 child_active=0 group_active=8 nextevt=3103000000 next_expiry=2934000000 child_evt_expiry=0 child_evtcpu=0

[  236.377222]   <idle>-0         0dn... 2928471us : tmigr_cpu_active: cpu=0 parent=aecb05cb wakeup=9223372036854775807
[  236.387765]   <idle>-0         0dn... 2928471us : tmigr_group_set_cpu_active: group=aecb05cb lvl=0 numa=0 active=9 migrator=8 parent=00000000 childmask=1

[  236.401526]   <idle>-0         0d.... 2928477us : tmigr_update_events: child=00000000 group=aecb05cb group_lvl=0 child_active=0 group_active=8 nextevt=3103000000 next_expiry=2934000000 child_evt_expiry=0 child_evtcpu=0
[  236.420940]   <idle>-0         0d.... 2928478us : tmigr_group_set_cpu_inactive: group=aecb05cb lvl=0 numa=0 active=8 migrator=8 parent=00000000 childmask=1
[  236.434874]   <idle>-0         0d.... 2928478us : tmigr_cpu_idle: cpu=0 parent=aecb05cb nextevt=3103000000 wakeup=9223372036854775807

[  236.446896]   <idle>-0         3d.... 2929469us : tmigr_group_set_cpu_inactive: group=aecb05cb lvl=0 numa=0 active=0 migrator=ff parent=00000000 childmask=8
[  236.460916]   <idle>-0         3d.... 2929470us : tmigr_cpu_idle: cpu=3 parent=aecb05cb nextevt=9223372036854775807 wakeup=9223372036854775807
[  236.473721]   <idle>-0         3d.... 2934471us : tmigr_cpu_new_timer_idle: cpu=3 parent=aecb05cb nextevt=9223372036854775807 wakeup=9223372036854775807

CPU3 is the last active CPU and goes idle. So it should take care of the
pending events, but it does not.

This is the next trace entry where CPU0 magically comes back to life.

[  236.487393]   <idle>-0         0d.s.. 162001359us : timer_cancel: timer=8c725d84

8ca1836769d758e4fbf5851bb81e181c52193f5d is related, but dos not fully
explain the fail. I haven't yet spotted where this goes into lala land.