Date: Thu, 5 Feb 2015 11:28:05 +0000
From: Mark Rutland <mark.rutland@arm.com>
To: Russell King - ARM Linux <linux@arm.linux.org.uk>
Cc: Krzysztof Kozlowski <k.kozlowski@samsung.com>,
        "linux-arm-kernel@lists.infradead.org" 
	<linux-arm-kernel@lists.infradead.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "paulmck@linux.vnet.ibm.com" <paulmck@linux.vnet.ibm.com>,
        Arnd Bergmann <arnd@arndb.de>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>,
        Marek Szyprowski <m.szyprowski@samsung.com>,
        Stephen Boyd <sboyd@codeaurora.org>,
        Catalin Marinas <Catalin.Marinas@arm.com>,
        Will Deacon <Will.Deacon@arm.com>
Subject: Re: [PATCH v2] ARM: Don't use complete() during __cpu_die
Message-ID: <20150205112805.GE11344@leverpostej>
References: <1423131270-24047-1-git-send-email-k.kozlowski@samsung.com>
 <20150205105035.GL8656@n2100.arm.linux.org.uk>
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Hi Russell,

On Thu, Feb 05, 2015 at 10:50:35AM +0000, Russell King - ARM Linux wrote:
> On Thu, Feb 05, 2015 at 11:14:30AM +0100, Krzysztof Kozlowski wrote:
> > The complete() should not be used on offlined CPU. Rewrite the
> > wait-complete mechanism with wait_on_bit_timeout().
> 
> Yuck.
> 
> I think that the IPI idea would be far better, and a much smaller patch.
> We can continue using the completions, but instead of running the
> completion on the dying CPU, the dying CPU triggers an IPI which does
> the completion on the requesting CPU.

This does look _much_ nicer than the bitmask approach.

[...]

> diff --git a/arch/arm/kernel/smp.c b/arch/arm/kernel/smp.c
> index 194df2f1aa87..c623e27a9c85 100644
> --- a/arch/arm/kernel/smp.c
> +++ b/arch/arm/kernel/smp.c
> @@ -73,6 +73,9 @@ enum ipi_msg_type {
>  	IPI_IRQ_WORK,
>  	IPI_COMPLETION,
>  	IPI_CPU_BACKTRACE,
> +#ifdef CONFIG_HOTPLUG_CPU
> +	IPI_CPU_DEAD,
> +#endif
>  };

[...]

>  static const char *ipi_types[NR_IPI] __tracepoint_string = {
>  #define S(x,s)	[x] = s
>  	S(IPI_WAKEUP, "CPU wakeup interrupts"),

We'll probably want to add an entry here ("CPU teardown interrupts"?),
and bump NR_IPI in asm/hardirq.h.

Thanks,
Mark.
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