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

[Florian Fainelli <f.fainelli@gmail.com>]

On 3/14/24 11:51, Boqun Feng wrote:
> On Thu, Mar 14, 2024 at 11:35:23AM -0700, Florian Fainelli wrote:
>> 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
> 
> FWIW, the trace point is still not enabled:
> 
> [    0.000000] Failed to enable trace event: timer_migration:*
> 
> you need this commit in master:
> 
> 	36e40df35d2c "timer_migration: Add tracepoints"
> 
> , which is one commit later than 7ee988770326 AFAICT

Argh, thanks Boqun, here is a new capture:

https://gist.github.com/ffainelli/cb562c1a60ef8e0e69e7d42143c48e8f

this one is does include the tmigr events. Thanks!
-- 
Florian