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

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Date: Wed, 13 Mar 2024 18:22:29 -0700
From: Florian Fainelli <f.fainelli@...il.com>
To: Linus Torvalds <torvalds@...ux-foundation.org>
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>, 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 3/13/2024 6:15 PM, Linus Torvalds wrote:
> On Wed, 13 Mar 2024 at 16:29, Florian Fainelli <f.fainelli@...il.com> wrote:
>>
>> On this specific commit 7ee988770326fca440472200c3eb58935fe712f6, there
>> is a 100% failure for at least 3 devices out of the 16 that are running
>> the test.
> 
> Hmm.  I have no idea what is going on, and the unimac-mdio probe
> function (one of the things that seem to take forever on your setup)
> looks fairly simple.
> 
> There doesn't even seem to be any timers involved.
> 
> That said - one of the things it does is
> 
>    unimac_mdio_probe ->
>      unimac_mdio_clk_set ->
>        clk_prepare_enable
> 
> and maybe that's a pattern, because you report that
> brcm_pcie_resume_noirq is another problem spot (on resume).
> 
> And guess what brcm_pcie_resume_noirq() does?
> 
> Yup. clk_prepare_enable().
> 
> So I'm wondering if there's some interaction with some clock driver?
> That might explain why it shows up on some arm platforms but not
> elsewhere.
> 
> I may be barking *entirely* up the wrong tree, though. I was just
> looking at that unimac probe and going "there's absolutely _nothing_
> timer-related here" and that clk thing looked like it might at least
> have _some_ relevance.

FWIW, we use the clk-scmi.c driver and the implementation of the SCMI 
platform/server resides in the ARM EL3 trusted firmware, that also has 
not changed. Ultimately this results in an ARM SMC call made to the 
firmware after having posted some SCMI message in a shared memory 
region. None of that has changed or is new, but it does also require me 
to look drivers/firmware/arm_scmi/ for possible changes.

Thanks!
-- 
Florian