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Mon, 15 Jun 2020 09:35:05 -0700 (PDT) Subject: Re: [PATCH v2] spi: bcm2835: Enable shared interrupt support To: Mark Brown , Robin Murphy References: <20200604212819.715-1-f.fainelli@gmail.com> <142d48ae-2725-1368-3e11-658449662371@arm.com> <20200605132037.GF5413@sirena.org.uk> <2e371a32-fb52-03a2-82e4-5733d9f139cc@arm.com> <06342e88-e130-ad7a-9f97-94f09156f868@arm.com> <20200608112840.GC4593@sirena.org.uk> From: Florian Fainelli Message-ID: Date: Mon, 15 Jun 2020 09:34:58 -0700 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:68.0) Gecko/20100101 Firefox/68.0 Thunderbird/68.9.0 MIME-Version: 1.0 In-Reply-To: <20200608112840.GC4593@sirena.org.uk> Content-Language: en-US X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200615_093508_256571_BA8F5F8E X-CRM114-Status: GOOD ( 13.59 ) 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: "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" , Florian Fainelli , Scott Branden , Ray Jui , linux-kernel@vger.kernel.org, Rob Herring , "open list:SPI SUBSYSTEM" , Nicolas Saenz Julienne , lukas@wunner.de, "maintainer:BROADCOM BCM281XX/BCM11XXX/BCM216XX ARM ARCHITE..." , "moderated list:BROADCOM BCM2711/BCM2835 ARM ARCHITECTURE" , Martin Sperl , "moderated list:BROADCOM BCM2711/BCM2835 ARM ARCHITECTURE" Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 6/8/2020 4:28 AM, Mark Brown wrote: > On Mon, Jun 08, 2020 at 12:11:11PM +0100, Robin Murphy wrote: > >> Again, 2 cycles. The overhead of a static key alone is at least 50% of that. >> And that's not even considering whether the change in code layout caused by >> doubling up the IRQ handler might affect I-cache or branch predictor >> behaviour, where a single miss stands to more than wipe out any perceived >> saving. And all in code that has at least one obvious inefficiency left on >> the table either way. > >> This thread truly epitomises Knuth's "premature optimisation" quote... ;) > > In fairness the main reason this driver is so heavily tuned already (and > has lead to some really nice improvements in the core) is that there are > a number of users hitting 100% CPU utilization driving SPI devices on > some of the older RPi hardware, IIRC around IIO type applications > mostly. I do tend to agree that this particular optimization is a bit > marginal but there has been a lot of effort put into this. OK, so this has been dropped for spi/for-next right? How do we move from there? -- Florian _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel