linux-kernel - Re: question about the limited interrupt vector resource on a single cpu

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Date:   Wed, 6 Jun 2018 19:44:38 +0800
From:   Pingfan Liu <kernelfans@...il.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: question about the limited interrupt vector resource on a single cpu

On Wed, Jun 6, 2018 at 5:34 PM, Thomas Gleixner <tglx@...utronix.de> wrote:
> On Wed, 6 Jun 2018, Pingfan Liu wrote:
>
>> On Wed, Jun 6, 2018 at 5:15 PM, Thomas Gleixner <tglx@...utronix.de> wrote:
>> > On Wed, 6 Jun 2018, Pingfan Liu wrote:
>> >
>> >> For x86, there is around 200 vectors left for external device on a
>> >> single logic cpu.
>> >>
>> >> Is there any case that we exhaust them in real world, and is it worth to fix?
>> >
>> > Exhaustion is unlikely, but how would you fix it? The vector space per CPU
>> > is limited by hardware not software.
>> >
>> Playing some trick on iommu, we can use it to identify the irq requester.
>
> But what's the point? If you have more than 200 device interrupts on a
> single CPU, then you surely have other problems than that.
>
> What kind of problem are you trying to solve?
>
In kdump case,  normally we set nr_cpus=1 by default, and in some huge
system, it can exhaust vector space.
By this is easily to resolve by inc nr_cpus. Hence I post this
question to see whether there are other requirements to resolve such
case

Thanks,
Pingfan