From: Andy Shevchenko <andy.shevchenko@gmail.com>
To: Ray Jui <ray.jui@broadcom.com>
Cc: Andrew Murray <andrew.murray@arm.com>,
Srinath Mannam <srinath.mannam@broadcom.com>,
Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>,
Bjorn Helgaas <bhelgaas@google.com>,
Florian Fainelli <f.fainelli@gmail.com>,
Ray Jui <rjui@broadcom.com>, Rob Herring <robh+dt@kernel.org>,
Mark Rutland <mark.rutland@arm.com>,
Arnd Bergmann <arnd@arndb.de>,
bcm-kernel-feedback-list <bcm-kernel-feedback-list@broadcom.com>,
linux-pci@vger.kernel.org,
devicetree <devicetree@vger.kernel.org>,
linux-arm Mailing List <linux-arm-kernel@lists.infradead.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v3 2/6] PCI: iproc: Add INTx support with better modeling
Date: Wed, 4 Dec 2019 10:29:51 +0200 [thread overview]
Message-ID: <CAHp75VfyKAg4OhzUa4swGXOGTvJ5fVO8mhGSG=5HAUP__M-URQ@mail.gmail.com> (raw)
In-Reply-To: <40fffa66-4b06-a851-84c2-4de36d5c6777@broadcom.com>
On Wed, Dec 4, 2019 at 12:09 AM Ray Jui <ray.jui@broadcom.com> wrote:
> On 12/3/19 11:27 AM, Andy Shevchenko wrote:
> > On Tue, Dec 3, 2019 at 5:55 PM Andrew Murray <andrew.murray@arm.com> wrote:
> >> On Tue, Dec 03, 2019 at 10:27:02AM +0530, Srinath Mannam wrote:
> >
> >>> + /* go through INTx A, B, C, D until all interrupts are handled */
> >>> + do {
> >>> + status = iproc_pcie_read_reg(pcie, IPROC_PCIE_INTX_CSR);
> >>
> >> By performing this read once and outside of the do/while loop you may improve
> >> performance. I wonder how probable it is to get another INTx whilst handling
> >> one?
> >
> > May I ask how it can be improved?
> > One read will be needed any way, and so does this code.
> >
>
> I guess the current code will cause the IPROC_PCIE_INTX_CSR register to
> be read TWICE, if it's ever set to start with.
>
> But then if we do it outside of the while loop, if we ever receive an
> interrupt while servicing one, the interrupt will still need to be
> serviced, and in this case, it will cause additional context switch
> overhead by going out and back in the interrupt context.
>
> My take is that it's probably more ideal to leave this portion of code
> as it is.
Can't we simple drop a do-while completely and leave only
for_each_set_bit() loop?
>
> >>> + for_each_set_bit(bit, &status, PCI_NUM_INTX) {
> >>> + virq = irq_find_mapping(pcie->irq_domain, bit);
> >>> + if (virq)
> >>> + generic_handle_irq(virq);
> >>> + else
> >>> + dev_err(dev, "unexpected INTx%u\n", bit);
> >>> + }
> >>> + } while ((status & SYS_RC_INTX_MASK) != 0);
> >
--
With Best Regards,
Andy Shevchenko
next prev parent reply other threads:[~2019-12-04 8:30 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-12-03 4:57 [PATCH v3 0/6] PAXB INTx support with proper model Srinath Mannam
2019-12-03 4:57 ` [PATCH v3 1/6] dt-bindings: pci: Update iProc PCI binding for INTx support Srinath Mannam
2019-12-03 19:19 ` Rob Herring
2019-12-03 4:57 ` [PATCH v3 2/6] PCI: iproc: Add INTx support with better modeling Srinath Mannam
2019-12-03 15:55 ` Andrew Murray
2019-12-03 19:27 ` Andy Shevchenko
2019-12-03 22:09 ` Ray Jui
2019-12-04 8:29 ` Andy Shevchenko [this message]
2019-12-04 16:07 ` Andrew Murray
2019-12-04 18:36 ` Ray Jui
2019-12-06 9:44 ` Srinath Mannam
2019-12-03 4:57 ` [PATCH v3 3/6] arm: dts: Change PCIe INTx mapping for Cygnus Srinath Mannam
2019-12-03 4:57 ` [PATCH v3 4/6] arm: dts: Change PCIe INTx mapping for NSP Srinath Mannam
2019-12-03 4:57 ` [PATCH v3 5/6] arm: dts: Change PCIe INTx mapping for HR2 Srinath Mannam
2019-12-03 4:57 ` [PATCH v3 6/6] arm64: dts: Change PCIe INTx mapping for NS2 Srinath Mannam
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