Date: Wed, 13 Mar 2024 15:04:26 -0700
From: Florian Fainelli <f.fainelli@...il.com>
To: "Russell King (Oracle)" <linux@...linux.org.uk>
Cc: 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,
 frederic@...nel.org, 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 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.

> 
> The last straw I can attempt to grasp at is maybe this has something to
> do with an inappropriate data type being used - maybe something in the
> timer code that the blamed commit changes that a 32-bit type is too
> small?
> 
-- 
Florian

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