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Mon, 21 Sep 2026 10:05:01 -0700 (PDT) From: Navon John Lukose To: Mika Westerberg Cc: Andi Shyti , linux-i2c@vger.kernel.org, Andy Shevchenko , linux-kernel@vger.kernel.org Subject: Re: [PATCH] i2c: designware: size the RX FIFO threshold to the queued transfer Date: Mon, 21 Sep 2026 22:34:56 +0530 Message-ID: <20260921170456.53354-1-navonjohnlukose@gmail.com> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260921120526.GV106095@black.igk.intel.com> References: <20260919232647.448748-1-navonjohnlukose@gmail.com> <20260921120526.GV106095@black.igk.intel.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit On Mon, Sep 21, 2026 at 02:05:26PM +0200, Mika Westerberg wrote: > I'm slightly worried about the latency increase here and the fact that > HIDIOCGINPUT is pretty much same as HID_REQ_GET_REPORT so it's not only > hidraw that is affected but everything else using HID_REQ_GET_REPORT as > well. You are right, it is every HID_REQ_GET_REPORT user, not just hidraw. The main motivation for this patch was cutting the wakeups from the interrupts, and I should have made that clearer. The /dev/cpu_dma_latency line was just to measure where the extra latency comes from. What the wakeups cost, measured with a 21-byte HID GET_REPORT at 142 Hz pinned to one CPU, display off, 32 reps per arm in randomized order: psys W idle 1.87 +/- 0.28 patched 2.53 +/- 0.17 stock 4.11 +/- 0.44 Against the idle floor the polling costs 2.24 W without the patch and 0.66 W with it. Paired saving 1.58 W, 95% CI [1.42, 1.75]. So the added exit latency is the package idling deeper than it can when the controller interrupts once per received byte.