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

Florian Fainelli
2024-03-14T18:35:25Z

On 3/14/24 03:41, Frederic Weisbecker wrote:
> 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.

Here is another log with timer_migration:

https://gist.github.com/ffainelli/237a5f9928850d6d8900d1f36da45aee
--
Florian