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

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Date:   Fri, 21 May 2021 09:46:20 -0400
From:   Nitesh Lal <nilal@...hat.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Jesse Brandeburg <jesse.brandeburg@...el.com>,
        Robin Murphy <robin.murphy@....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,
        "frederic@...nel.org" <frederic@...nel.org>,
        "juri.lelli@...hat.com" <juri.lelli@...hat.com>,
        Alex Belits <abelits@...vell.com>,
        "linux-api@...r.kernel.org" <linux-api@...r.kernel.org>,
        "bhelgaas@...gle.com" <bhelgaas@...gle.com>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        "rostedt@...dmis.org" <rostedt@...dmis.org>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "sfr@...b.auug.org.au" <sfr@...b.auug.org.au>,
        "stephen@...workplumber.org" <stephen@...workplumber.org>,
        "rppt@...ux.vnet.ibm.com" <rppt@...ux.vnet.ibm.com>,
        "jinyuqi@...wei.com" <jinyuqi@...wei.com>,
        "zhangshaokun@...ilicon.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

On Fri, May 21, 2021 at 7:56 AM Thomas Gleixner <tglx@...utronix.de> wrote:
>
> 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()

Ah yes! my bad. _force_ doesn't check the mask against the online CPUs.
Hmm, I didn't realize that you also added irq_set_affinity_and_hint()
in your last patchset.

>
> >> 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

Right.

> 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. :)

Ack will start looking into this.


--
Thanks
Nitesh