linux-kernel - Re: [v4.1.10-rt10][PATCH 1/2] genirq: introduce new generic_handle_irq_rt

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Message-ID: <56391694.3030105@linutronix.de>
Date:	Tue, 3 Nov 2015 21:18:28 +0100
From:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:	Thomas Gleixner <tglx@...utronix.de>,
	Grygorii Strashko <grygorii.strashko@...com>
Cc:	linux-rt-users@...r.kernel.org, linux-kernel@...r.kernel.org,
	Sekhar Nori <nsekhar@...com>
Subject: Re: [v4.1.10-rt10][PATCH 1/2] genirq: introduce new
 generic_handle_irq_rt_wa() api

On 11/03/2015 08:51 PM, Thomas Gleixner wrote:
>> where MAX_MSI_IRQS = 32 now, but potentially can be increased up to 256.
> 
> And you really oversimplified the code above. The reality is:
> 
>     for (i = 0; i < MAX_MSI_CTRLS: i++) {
>     	u32 status = read_msi_ctrl(i);
> 
> 	for_each_bit(status)
> 		handle_irq();
>     }
> 
> So sure, the worst case here is MAX_MSI_CTRLS * 32, but if all
> possible 256 MSI interrupts are pending at the same time, you have
> other problems than that.

With threaded interrupts we would have 256 invocations of
wake_up_process() so nothing should take ages.

> Thanks,
> 
> 	tglx

Sebastian
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