linux-kernel - Re: [PATCH v3 2/4] drm/i915/pmu: Use kstat

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Message-ID: <20201208095432.GA44672@kernel.org>
Date:   Tue, 8 Dec 2020 11:54:32 +0200
From:   Jarkko Sakkinen <jarkko@...nel.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Jerry Snitselaar <jsnitsel@...hat.com>,
        linux-kernel@...r.kernel.org, linux-integrity@...r.kernel.org,
        intel-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Peter Huewe <peterhuewe@....de>,
        James Bottomley <James.Bottomley@...senpartnership.com>,
        Matthew Garrett <mjg59@...gle.com>,
        Hans de Goede <hdegoede@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH v3 2/4] drm/i915/pmu: Use kstat_irqs to get interrupt
 count

On Sun, Dec 06, 2020 at 10:33:09PM +0100, Thomas Gleixner wrote:
> On Sun, Dec 06 2020 at 17:38, Thomas Gleixner wrote:
> > On Fri, Dec 04 2020 at 18:43, Jerry Snitselaar wrote:
> >> Now that kstat_irqs is exported, get rid of count_interrupts in
> >> i915_pmu.c
> >
> > May I ask why this has been merged in the first place?
> >
> > Nothing in a driver has ever to fiddle with the internals of an irq
> > descriptor. We have functions for properly accessing them. Just because
> > C allows to fiddle with everything is not a justification. If the
> > required function is not exported then adding the export with a proper
> > explanation is not asked too much.
> >
> > Also this lacks protection or at least a comment why this can be called
> > safely and is not subject to a concurrent removal of the irq descriptor.
> > The same problem exists when calling kstat_irqs(). It's even documented
> > at the top of the function.
> 
> And as pointed out vs. that TPM thing this really could have been a
> trivial
> 
>     i915->irqs++;
> 
> in the interrupt handler and a read of that instead of iterating over
> all possible cpus and summing it up. Oh well...

I'm fine with that. 

> Thanks,
> 
>         tglx

/Jarkko