linux-kernel - Re: [PATCH tip:irq/core v1] genirq: remove auto-set of the mask when setting the hint

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Message-ID: <87y2cddtxb.ffs@nanos.tec.linutronix.de>
Date:   Mon, 17 May 2021 21:47:12 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Nitesh Lal <nilal@...hat.com>, Robin Murphy <robin.murphy@....com>
Cc:     Jesse Brandeburg <jesse.brandeburg@...el.com>,
        "frederic\@kernel.org" <frederic@...nel.org>,
        "juri.lelli\@redhat.com" <juri.lelli@...hat.com>,
        Marcelo Tosatti <mtosatti@...hat.com>,
        Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org,
        intel-wired-lan@...ts.osuosl.org, jbrandeb@...nel.org,
        Alex Belits <abelits@...vell.com>,
        "linux-api\@vger.kernel.org" <linux-api@...r.kernel.org>,
        "bhelgaas\@google.com" <bhelgaas@...gle.com>,
        "linux-pci\@vger.kernel.org" <linux-pci@...r.kernel.org>,
        "rostedt\@goodmis.org" <rostedt@...dmis.org>,
        "peterz\@infradead.org" <peterz@...radead.org>,
        "davem\@davemloft.net" <davem@...emloft.net>,
        "akpm\@linux-foundation.org" <akpm@...ux-foundation.org>,
        "sfr\@canb.auug.org.au" <sfr@...b.auug.org.au>,
        "stephen\@networkplumber.org" <stephen@...workplumber.org>,
        "rppt\@linux.vnet.ibm.com" <rppt@...ux.vnet.ibm.com>,
        "jinyuqi\@huawei.com" <jinyuqi@...wei.com>,
        "zhangshaokun\@hisilicon.com" <zhangshaokun@...ilicon.com>,
        netdev@...r.kernel.org, chris.friesen@...driver.com,
        Marc Zyngier <maz@...nel.org>
Subject: Re: [PATCH tip:irq/core v1] genirq: remove auto-set of the mask when setting the hint

Nitesh,

On Mon, May 17 2021 at 14:21, Nitesh Lal wrote:
> On Mon, May 17, 2021 at 1:26 PM Robin Murphy <robin.murphy@....com> wrote:
>
> We can use irq_set_affinity() to set the hint mask as well, however, maybe
> there is a specific reason behind separating those two in the
> first place (maybe not?).

Yes, because kernel side settings might overwrite the hint.

> But even in this case, we have to either modify the PMU drivers' IRQs
> affinity from the userspace or we will have to make changes in the existing
> request_irq code path.

Adjusting them from user space does not work for various reasons,
especially CPU hotplug.

> I am not sure about the latter because we already have the required controls
> to adjust the device IRQ mask (by using default_smp_affinity or by modifying
> them manually).

default_smp_affinity does not help at all and there is nothing a module
can modify manually.

I'll send out a patch series which cleans that up soon.

Thanks,

        tglx