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

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Message-ID: <ZfLUU+XuQC7W79tf@lothringen>
Date: Thu, 14 Mar 2024 11:41:23 +0100
From: Frederic Weisbecker <frederic@...nel.org>
To: Florian Fainelli <f.fainelli@...il.com>
Cc: "Russell King (Oracle)" <linux@...linux.org.uk>,
	Joel Fernandes <joel@...lfernandes.org>,
	Boqun Feng <boqun.feng@...il.com>,
	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, tglx@...utronix.de,
	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 Wed, Mar 13, 2024 at 08:44:07PM -0700, Florian Fainelli wrote:
> 
> 
> On 3/13/2024 3:52 PM, Frederic Weisbecker wrote:
> > On Wed, Mar 13, 2024 at 03:04:26PM -0700, Florian Fainelli wrote:
> > > On 3/13/24 14:59, Russell King (Oracle) wrote:
> > > > On Wed, Mar 13, 2024 at 02:30:43PM -0700, Florian Fainelli wrote:
> > > > > I will try to provide multiple answers for the sake of everyone having the
> > > > > same context. Responding to Linus' specifically and his suggestion to use
> > > > > "initcall_debug", this is what it gave me:
> > > > > 
> > > > > [    6.970669] ata1: SATA link down (SStatus 0 SControl 300)
> > > > > [  166.136366] probe of unimac-mdio-0:01 returned 0 after 159216218 usecs
> > > > > [  166.142931] unimac-mdio unimac-mdio.0: Broadcom UniMAC MDIO bus
> > > > > [  166.148900] probe of unimac-mdio.0 returned 0 after 159243553 usecs
> > > > > [  166.155820] probe of f0480000.ethernet returned 0 after 159258794 usecs
> > > > > [  166.166427] ehci-brcm f0b00300.ehci_v2: EHCI Host Controller
> > > > > 
> > > > > Also got another occurrence happening resuming from suspend to DRAM with:
> > > > > 
> > > > > [   22.570667] brcmstb-dpfe 9932000.dpfe-cpu: PM: calling
> > > > > platform_pm_resume+0x0/0x54 @ 1574, parent: rdb
> > > > > [  181.643809] brcmstb-dpfe 9932000.dpfe-cpu: PM:
> > > > > platform_pm_resume+0x0/0x54 returned 0 after 159073134 usecs
> > > > > 
> > > > > and also with the PCIe root complex driver:
> > > > > 
> > > > > [   18.266279] brcm-pcie f0460000.pcie: PM: calling
> > > > > brcm_pcie_resume_noirq+0x0/0x164 @ 1597, parent: platform
> > > > > [  177.457219] brcm-pcie f0460000.pcie: clkreq-mode set to default
> > > > > [  177.457225] brcm-pcie f0460000.pcie: link up, 2.5 GT/s PCIe x1 (!SSC)
> > > > > [  177.457231] brcm-pcie f0460000.pcie: PM: brcm_pcie_resume_noirq+0x0/0x164
> > > > > returned 0 after 159190939 usecs
> > > > > [  177.457257] pcieport 0000:00:00.0: PM: calling
> > > > > pci_pm_resume_noirq+0x0/0x160 @ 33, parent: pci0000:00
> > > > > 
> > > > > Surprisingly those drivers are consistently reproducing the failures I am
> > > > > seeing so at least this gave me a clue as to where the problem is.
> > > > > 
> > > > > There were no changes to drivers/net/ethernet/broadcom/genet/, the two
> > > > > changes done to drivers/net/mdio/mdio-bcm-unimac.c are correct, especially
> > > > > the read_poll_timeout() conversion is correct, we properly break out of the
> > > > > loop. The initial delay looked like a good culprit for a little while, but
> > > > > it is not used on the affected platforms because instead we provide a
> > > > > callback and we have an interrupt to signal the completion of a MDIO
> > > > > operation, therefore unimac_mdio_poll() is not used at all. Finally
> > > > > drivers/memory/brcmstb_dpfe.c also received a single change which is not
> > > > > functional here (.remove function change do return void).
> > > > > 
> > > > > I went back to a manual bisection and this time I believe that I have a more
> > > > > plausible candidate with:
> > > > > 
> > > > > 7ee988770326fca440472200c3eb58935fe712f6 ("timers: Implement the
> > > > > hierarchical pull model")
> > > > 
> > > > I haven't understood the code there yet, and how it would interact with
> > > > arch code, but one thing that immediately jumps out to me is this:
> > > > 
> > > > "    As long as a CPU is busy it expires both local and global timers. When a
> > > >       CPU goes idle it arms for the first expiring local timer."
> > > > 
> > > > So are local timers "armed" when they are enqueued while the cpu is
> > > > "busy" during initialisation, and will they expire, and will that
> > > > expiry be delivered in a timely manner?
> > > > 
> > > > If not, this commit is basically broken, and would be the cause of the
> > > > issue you are seeing. For the mdio case, we're talking about 2ms
> > > > polling. For the dpfe case, it looks like we're talking about 1ms
> > > > sleeps. I'm guessing that these end up being local timers.
> > > > 
> > > > Looking at pcie-brcmstb, there's a 100ms msleep(), and then a polling
> > > > for link up every 5ms - if the link was down and we msleep(5) I wonder
> > > > if that's triggering the same issue.
> > > > 
> > > > Why that would manifest itself on 32-bit but not 64-bit Arm, I can't
> > > > say. I would imagine that the same hardware timer driver is being used
> > > > (may be worth checking DT.) The same should be true for the interrupt
> > > > driver as well. There's been no changes in that code.
> > > 
> > > I just had it happen with ARM64 I was plagued by:
> > > 
> > > https://lore.kernel.org/lkml/87wmqrjg8n.fsf@somnus/T/
> > > 
> > > and my earlier bisections somehow did not have ARM64 fail, so I thought it
> > > was immune but it fails with about the same failure rate as ARM 32-bit.
> > 
> > Can you please boot with:
> > 
> >      trace_event=timer_migration,timer_start,timer_expire_entry,timer_cancel
> > 
> > And add the following and give us the resulting output in dmesg?
> 
> Here are two logs from two different systems that exposed the problem on
> boot:
> 
> https://gist.github.com/ffainelli/f0834c52ef6320c9216d879ca29a4b81
> https://gist.github.com/ffainelli/dc838883edb925a77d8eb34c0fe95be0

Thanks! Unfortunately like Thomas pointed out, I'm missing the timer_migration
events. My fault, can you retry with this syntax?

	trace_event=timer_migration:*,timer_start,timer_expire_entry,timer_cancel

Though it's fairly possible that timer migration is not enabled at this point
as it's a late initcall. But we better not miss its traces otherwise.



> thanks!
> -- 
> Florian
>