From: "Paul E. McKenney" <paulmck@kernel.org>
To: Qian Cai <cai@lca.pw>
Cc: rcu@vger.kernel.org, LKML <linux-kernel@vger.kernel.org>
Subject: Re: Boot warning at rcu_check_gp_start_stall()
Date: Tue, 21 Jan 2020 06:19:23 -0800 [thread overview]
Message-ID: <20200121141923.GP2935@paulmck-ThinkPad-P72> (raw)
In-Reply-To: <D7FEEB19-B519-4AC6-ABA4-250200E2A4E9@lca.pw>
On Tue, Jan 21, 2020 at 06:45:32AM -0500, Qian Cai wrote:
>
>
> > On Jan 21, 2020, at 12:09 AM, Paul E. McKenney <paulmck@kernel.org> wrote:
> >
> > This is what you get when a grace period has been requested, but does
> > not start within 21 seconds or so. The "->state: 0x1ffff" is a new one
> > on me -- that normally happens only before RCU's grace-period kthread
> > has been spawned. But by 97 seconds after boot, it should definitely
> > already be up and running.
> >
> > Is the system responsive at this point?
>
> Yes, it works fine.
>
> > Except... Why is it taking 96 seconds for the system to get to the point
> > where it prints "Dentry cache hash table entries:"? That happens at 0.139
> > seconds on my laptop. And at about the same time on a much larger system.
> >
> > I could easily imagine that all sorts of things would break when boot
> > takes that long.
>
> I suppose the kernel has CONFIG_EFI_PGT_DUMP=y, so it takes a while to run just before rcu_check_gp_start_stall().
New one on me!
One approach would be to boot with rcupdate.rcu_cpu_stall_timeout=300,
which would allow more time.
Longer term, I could suppress this warning during boot when
CONFIG_EFI_PGT_DUMP=y, but that sounds quite specific. Alternatively,
I could provide a Kconfig option that suppressed this during boot
that was selected by whatever long-running boot-time Kconfig option
needed it. Yet another approach would be for long-running operations
like efi_dump_pagetable() to suppress stalls on entry and re-enable them
upon exit.
Thoughts?
Thanx, Paul
next prev parent reply other threads:[~2020-01-21 14:19 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-21 4:25 Qian Cai
2020-01-21 5:09 ` Paul E. McKenney
2020-01-21 11:45 ` Qian Cai
2020-01-21 14:19 ` Paul E. McKenney [this message]
2020-01-21 14:37 ` Qian Cai
2020-01-21 16:15 ` Paul E. McKenney
2020-01-21 19:09 ` Qian Cai
2020-01-21 20:46 ` Paul E. McKenney
2020-01-22 4:16 ` Qian Cai
2020-01-22 5:07 ` Paul E. McKenney
2020-01-22 5:20 ` Qian Cai
2020-01-22 16:50 ` Paul E. McKenney
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