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

From: Nitesh Lal <nilal@redhat.com>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: Jesse Brandeburg <jesse.brandeburg@intel.com>,
	Robin Murphy <robin.murphy@arm.com>,
	Marcelo Tosatti <mtosatti@redhat.com>,
	Ingo Molnar <mingo@kernel.org>,
	linux-kernel@vger.kernel.org, intel-wired-lan@lists.osuosl.org,
	jbrandeb@kernel.org, "frederic@kernel.org" <frederic@kernel.org>,
	"juri.lelli@redhat.com" <juri.lelli@redhat.com>,
	Alex Belits <abelits@marvell.com>,
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	Marc Zyngier <maz@kernel.org>,
	Neil Horman <nhorman@tuxdriver.com>,
	pjwaskiewicz@gmail.com
Subject: Re: [PATCH tip:irq/core v1] genirq: remove auto-set of the mask when setting the hint
Date: Fri, 21 May 2021 09:46:20 -0400	[thread overview]
Message-ID: <CAFki+LnKycMFYTGTswX9vpMepNiCW6BL5TFMTuKZSniab5=4SA@mail.gmail.com> (raw)
In-Reply-To: <87zgwo9u79.ffs@nanos.tec.linutronix.de>

On Fri, May 21, 2021 at 7:56 AM Thomas Gleixner <tglx@linutronix.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@redhat.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