linux-kernel - Re: [PATCH V4 3/3] Revert "ACPI, PCI, IRQ: separate ISA penalty calculation"

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Date:   Sat, 22 Oct 2016 18:59:18 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Sinan Kaya <okaya@...eaurora.org>
Cc:     linux-acpi@...r.kernel.org, rjw@...ysocki.net, bhelgaas@...gle.com,
        ravikanth.nalla@....com, linux@...nbow-software.org,
        timur@...eaurora.org, cov@...eaurora.org, jcm@...hat.com,
        alex.williamson@...hat.com, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>, linux-pci@...r.kernel.org,
        agross@...eaurora.org, Robert Moore <robert.moore@...el.com>,
        linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
        Lv Zheng <lv.zheng@...el.com>, linux-arm-msm@...r.kernel.org,
        wim@....tudelft.nl, devel@...ica.org,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-arm-kernel@...ts.infradead.org, Len Brown <lenb@...nel.org>
Subject: Re: [PATCH V4 3/3] Revert "ACPI, PCI, IRQ: separate ISA penalty
 calculation"

On Thu, Oct 20, 2016 at 07:58:57PM -0700, Sinan Kaya wrote:
> On 10/20/2016 7:31 PM, Bjorn Helgaas wrote:
> ...
> > And I don't think it fixes a user-visible problem, so it doesn't need
> > to be applied immediately.  I'm not sure this is worth doing by
> > itself; maybe it should wait until we can do more cleanup and think
> > about all these issues together?
> 
> It does fix the PCI_USING penalty assignment. 
> 
>                 if (link->irq.active && link->irq.active == irq)
>                          penalty += PIRQ_PENALTY_PCI_USING;
> 
> 
> If we drop this patch, then we need
> [PATCH V3 1/3] ACPI, PCI IRQ: add PCI_USING penalty for ISA interrupts
> 
> http://www.gossamer-threads.com/lists/linux/kernel/2547605
> 
> as somebody needs to increment the penalty with PCI_USING when IRQ is assigned
> for a given ISA IRQ.
> 
> We might as well take [PATCH V4 1/3], [PATCH V4 2/3] and [PATCH V3 1/3]
> for this regression.

It sounds like either V3 1/3 or V4 3/3 will fix the regression.  The
V3 1/3 patch is much smaller and essentially makes this piece look
like it did in v4.6.

The V4 3/3 patch removes acpi_irq_penalty_init() and compensates by
using acpi_irq_pci_sharing_penalty() for ISA IRQs again.  But
acpi_irq_penalty_init() added PIRQ_PENALTY_PCI_POSSIBLE for _CRS, and
only if there was no _PRS, while acpi_irq_pci_sharing_penalty() always
adds PIRQ_PENALTY_PCI_USING for _CRS, regardless of whether _PRS
exists.

Since V4 3/3 is so much bigger and makes this quite subtle change in
how _CRS is handled, I like V3 1/3 better.

Are we all set to go now?  I think I've acked the patches you
mentioned.

Bjorn