linux-kernel - Re: [PATCH] ARM: Support arch_irq_work

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Date:	Fri, 8 Nov 2013 12:06:55 -0800
From:	Olof Johansson <olof@...om.net>
To:	Stephen Boyd <sboyd@...eaurora.org>
Cc:	Kevin Hilman <khilman@...aro.org>,
	Russell King <linux@....linux.org.uk>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Maxime Ripard <maxime.ripard@...e-electrons.com>
Subject: Re: [PATCH] ARM: Support arch_irq_work_raise() via self IPIs

On Mon, Oct 28, 2013 at 11:00 PM, Stephen Boyd <sboyd@...eaurora.org> wrote:
> On 10/28, Kevin Hilman wrote:
>> Stephen Boyd <sboyd@...eaurora.org> writes:
>>
>> > This will allow the scheduler tick to be restarted if we're in
>> > full NOHZ mode.
>> >
>> > Cc: Kevin Hilman <khilman@...aro.org>
>> > Cc: Frederic Weisbecker <fweisbec@...il.com>
>> > Signed-off-by: Stephen Boyd <sboyd@...eaurora.org>
>>
>> Minor nit, but I'd prefer a more verbose changelog (I forget things
>> quickly and like to rely on changelogs for my memory.)  Probably worth
>> adding something like: "By default, irq_work is tied to the tick
>> processing (update_process_times()) but in full NOHZ mode, no tick means
>> no IRQ work.  In order for IRQ work to be done in full NOHZ mode, a
>> self-IPI is used to process IRQ work."
>>
>> Other than the changelog nit, patch looks good, feel free to add
>>
>> Reviewed-by: Kevin Hilman <khilman@...aro.org>
>>
>> If Russell is OK with this, it can go to his patch system.
>>
>
> Fair enough. This is what I came up with. I'll send it off to the
> patch tracker in about 12 hours if nobody else has anymore
> comments.
>
> ----8<-----
> ARM: Support arch_irq_work_raise() via self IPIs
>
> By default, IRQ work is run from the tick interrupt (see
> irq_work_run() in update_process_times()). When we're in full
> NOHZ mode, restarting the tick requires the use of IRQ work and
> if the only place we run IRQ work is in the tick interrupt we
> have an unbreakable cycle. Implement arch_irq_work_raise() via
> self IPIs to break this cycle and get the tick started again.
> Note that we implement this via IPIs which are only available on
> SMP builds. This shouldn't be a problem because full NOHZ is only
> supported on SMP builds anyway.
>
> Signed-off-by: Stephen Boyd <sboyd@...eaurora.org>
> Reviewed-by: Kevin Hilman <khilman@...aro.org>
> Cc: Frederic Weisbecker <fweisbec@...il.com>


Hm, so I think this just landed in -next, which seems... late for
3.13. Anyway, it causes boot failures on Cubieboards (Allwinner A10),
I just bisected it down to this patch (fails to boot
multi_v7_defconfig, no console output at all).

Unfortunately I'm not getting any debug_ll output from the board at
the moment, so I can't actually get to a panic stack or other error
info. :( I hope I can get back to you with one later today.


-Olof
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