linux-kernel - Re: [PATCH 1/2] genirq/msi, platform-msi: Adjust return value of msi_domain_prepare

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Date:   Mon, 29 May 2023 17:36:07 +0800
From:   Huacai Chen <chenhuacai@...il.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Marc Zyngier <maz@...nel.org>,
        Huacai Chen <chenhuacai@...ngson.cn>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        linux-kernel@...r.kernel.org, loongson-kernel@...ts.loongnix.cn,
        Xuefeng Li <lixuefeng@...ngson.cn>,
        Jiaxun Yang <jiaxun.yang@...goat.com>
Subject: Re: [PATCH 1/2] genirq/msi, platform-msi: Adjust return value of msi_domain_prepare_irqs()

Hi, Thomas,

On Mon, May 29, 2023 at 5:27 PM Thomas Gleixner <tglx@...utronix.de> wrote:
>
> On Sun, May 28 2023 at 20:07, Huacai Chen wrote:
> > On Sun, May 28, 2023 at 3:47 PM Marc Zyngier <maz@...nel.org> wrote:
> >>
> >> Being able to allocate MSIs is not a guarantee, and is always
> >> opportunistic. If some drivers badly fail because the they don't get
> >> the number of MSIs they need, then they need fixing.
> >
> > Yes, I know allocating MSIs is not a guarantee, and most existing
> > drivers will fallback to use legacy irqs when failed. However, as I
> > replied in an early mail, we want to do some proactive throttling in
> > the loongson-pch-msi irqchip driver, rather than consume msi vectors
> > aggressively. For example, if we have two NICs, we want both of them
> > to get 32 msi vectors; not one exhaust all available vectors, and the
> > other fallback to use legacy irq.
>
> By default you allow up to 256 interrupts to be allocated, right? So to
> prevent vector exhaustion, the admin needs to reboot the machine and set
> a command line parameter to limit this, right? As that parameter is not
> documented the admin is going to dice a number. That's impractical and
> just a horrible bandaid.
OK, I think I should update the documents in the new version.

Huacai
>
> Thanks,
>
>         tglx
>
>