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Tue, 03 Dec 2019 14:09:33 -0800 (PST) Subject: Re: [PATCH v3 2/6] PCI: iproc: Add INTx support with better modeling To: Andy Shevchenko , Andrew Murray References: <1575349026-8743-1-git-send-email-srinath.mannam@broadcom.com> <1575349026-8743-3-git-send-email-srinath.mannam@broadcom.com> <20191203155514.GE18399@e119886-lin.cambridge.arm.com> From: Ray Jui Message-ID: <40fffa66-4b06-a851-84c2-4de36d5c6777@broadcom.com> Date: Tue, 3 Dec 2019 14:09:22 -0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.2.1 MIME-Version: 1.0 In-Reply-To: Content-Language: en-US X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20191203_140935_150749_5F86C1C6 X-CRM114-Status: GOOD ( 16.50 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Mark Rutland , devicetree , Florian Fainelli , Arnd Bergmann , Ray Jui , Linux Kernel Mailing List , Rob Herring , Lorenzo Pieralisi , Srinath Mannam , linux-pci@vger.kernel.org, Bjorn Helgaas , bcm-kernel-feedback-list , linux-arm Mailing List Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 12/3/19 11:27 AM, Andy Shevchenko wrote: > On Tue, Dec 3, 2019 at 5:55 PM Andrew Murray 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. >>> + 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); > _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel