linux-kernel - Re: [PATCH 2/6] irq_work: Implement remote queueing

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Date:	Wed, 25 Jun 2014 16:27:52 +0530
From:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	Stephen Warren <swarren@...dotorg.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Eric Dumazet <eric.dumazet@...il.com>,
	Ingo Molnar <mingo@...nel.org>,
	Kevin Hilman <khilman@...aro.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Viresh Kumar <viresh.kumar@...aro.org>,
	"linux-next@...r.kernel.org" <linux-next@...r.kernel.org>
Subject: Re: [PATCH 2/6] irq_work: Implement remote queueing

On 06/25/2014 03:49 PM, Peter Zijlstra wrote:
> On Wed, Jun 25, 2014 at 03:24:11PM +0530, Srivatsa S. Bhat wrote:
>> Wait, that was a stupid idea. hotplug_cfd() already invokes irq_work_run
>> indirectly via flush_smp_call_function_queue(). So irq_work_cpu_notify()
>> doesn't need to invoke it again, AFAIU. So perhaps we can get rid of
>> irq_work_cpu_notify() altogether?
> 
> Just so...
> 
> getting up at 6am and sitting in an airport terminal doesn't seem to
> agree with me;

Haha :-)

> any more silly fail here?
> 

A few minor nits below..

> ---
> Subject: irq_work: Remove BUG_ON in irq_work_run()
> From: Peter Zijlstra <peterz@...radead.org>
> Date: Wed Jun 25 07:13:07 CEST 2014
> 
> Because of a collision with 8d056c48e486 ("CPU hotplug, smp: flush any
> pending IPI callbacks before CPU offline"), which ends up calling
> hotplug_cfd()->flush_smp_call_function_queue()->irq_work_run(), which
> is not from IRQ context.
> 
> And since that already calls irq_work_run() from the hotplug path,
> remove our entire hotplug handling.
> 
> Cc: Frederic Weisbecker <fweisbec@...il.com>
> Reported-by: Stephen Warren <swarren@...dotorg.org>
> Signed-off-by: Peter Zijlstra <peterz@...radead.org>
> Link: http://lkml.kernel.org/n/tip-busatzs2gvz4v62258agipuf@git.kernel.org
> ---
>  kernel/irq_work.c |   48 +++++-------------------------------------------
>  1 file changed, 5 insertions(+), 43 deletions(-)
> 
> Index: linux-2.6/kernel/irq_work.c
> ===================================================================
> --- linux-2.6.orig/kernel/irq_work.c
> +++ linux-2.6/kernel/irq_work.c
> @@ -160,20 +160,14 @@ static void irq_work_run_list(struct lli
>  	}
>  }
> 
> -static void __irq_work_run(void)
> -{
> -	irq_work_run_list(&__get_cpu_var(raised_list));
> -	irq_work_run_list(&__get_cpu_var(lazy_list));
> -}
> -
>  /*
> - * Run the irq_work entries on this cpu. Requires to be ran from hardirq
> - * context with local IRQs disabled.
> + * hotplug calls this through:
> + *  hotplug_cfs() -> flush_smp_call_function_queue()

s/hotplug_cfs/hotplug_cfd

>   */
> -void irq_work_run(void)
> +static void irq_work_run(void)

s/static//

>  {
> -	BUG_ON(!in_irq());
> -	__irq_work_run();
> +	irq_work_run_list(&__get_cpu_var(raised_list));
> +	irq_work_run_list(&__get_cpu_var(lazy_list));
>  }
>  EXPORT_SYMBOL_GPL(irq_work_run);

With those 2 changes, everything looks good to me.

Regards,
Srivatsa S. Bhat



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