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: <87zgwo9u79.ffs@nanos.tec.linutronix.de>
Date:   Fri, 21 May 2021 13:56:10 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Nitesh Lal <nilal@...hat.com>,
        Jesse Brandeburg <jesse.brandeburg@...el.com>,
        Robin Murphy <robin.murphy@....com>,
        Marcelo Tosatti <mtosatti@...hat.com>
Cc:     Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org,
        intel-wired-lan@...ts.osuosl.org, jbrandeb@...nel.org,
        "frederic\@kernel.org" <frederic@...nel.org>,
        "juri.lelli\@redhat.com" <juri.lelli@...hat.com>,
        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>,
        Neil Horman <nhorman@...driver.com>, pjwaskiewicz@...il.com
Subject: Re: [PATCH tip:irq/core v1] genirq: remove auto-set of the mask when setting the hint

Nitesh,

On Thu, May 20 2021 at 20:03, Nitesh Lal wrote:
> On Thu, May 20, 2021 at 5:57 PM Nitesh Lal <nilal@...hat.com> wrote:
>> I think here to ensure that we are not breaking any of the drivers we have
>> to first analyze all the existing drivers and understand how they are using
>> this API.
>> AFAIK there are three possible scenarios:
>>
>> - A driver use this API to spread the IRQs
>>   + For this case we should be safe considering the spreading is naturally
>>     done from the IRQ subsystem itself.
>
> Forgot to mention another thing in the above case is to determine whether
> it is true for all architectures or not as Thomas mentioned.

Yes.

>>
>> - A driver use this API to actually set the hint
>>   + These drivers should have no functional impact because of this revert

Correct.


>> - Driver use this API to force a certain affinity mask
>>   + In this case we have to replace the API with the irq_force_affinity()

irq_set_affinity() or irq_set_affinity_and_hint()

>> I can start looking into the individual drivers, however, testing them will
>> be a challenge.

The only way to do that is to have the core infrastructure added and
then send patches changing it in the way you think. The relevant
maintainers/developers should be able to tell you when your analysis
went south. :)

Been there, done that. It's just lots of work :)

Thanks,

        tglx