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([2600:6c56:7d00:582f::64e]) by smtp.googlemail.com with ESMTPSA id 00721157ae682-796401a19c6sm48506387b3.10.2026.02.09.15.24.15 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 09 Feb 2026 15:24:15 -0800 (PST) Message-ID: <83e65606-cbbf-421a-9de6-9e39a7d872dd@gmail.com> Date: Mon, 9 Feb 2026 17:24:13 -0600 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 0/1] cpuidle: menu: Fix high wakeup latency on modern platforms To: "Ionut Nechita (Sunlight Linux)" , christian.loehle@arm.com Cc: daniel.lezcano@linaro.org, ionut_n2001@yahoo.com, linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org, rafael@kernel.org References: <20260122080937.22347-2-sunlightlinux@gmail.com> <54478318-cbee-46f2-9ff1-9c0ae15a89ab@arm.com> <20260126201943.11505-2-sunlightlinux@gmail.com> Content-Language: en-US From: Russell Haley In-Reply-To: <20260126201943.11505-2-sunlightlinux@gmail.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 1/26/26 2:19 PM, Ionut Nechita (Sunlight Linux) wrote: > I considered PM QoS and /dev/cpu_dma_latency, but they have limitations > for this use case: > > 1. Global PM QoS affects all cores, not just the isolated ones > 2. Per-task PM QoS requires application modifications > 3. /dev/cpu_dma_latency is system-wide, not per-core > > For isolated cores with NOHZ_FULL in a realtime environment, we want > the governor to make smarter decisions based on actual predicted idle > time rather than relying on next_timer_ns which can be arbitrarily large > on tickless cores. > In case it helps, you can write "1" to /sys/devices/system/cpu/cpu*/cpuidle/state*/disable to lock out any idle states that are too deep. That's per-core, although it's not as "crash clean" as holding an FD for /dev/cpu_dma_latency. - Russell Haley