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

Florian Fainelli
2024-03-14T03:44:12Z

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!
--
Florian