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Mon, 14 Apr 2025 01:06:09 -0700 (PDT) X-Google-Smtp-Source: AGHT+IEY3/6voGKwFboLlpb/71hND3KDiKWzqFF3yYwomw1Ik9ctTfuUb+eBUwc8X4YOOTrNv1+dzA== X-Received: by 2002:a05:6000:18af:b0:39c:119f:27c4 with SMTP id ffacd0b85a97d-39ea5212fd6mr8390553f8f.30.1744617968780; Mon, 14 Apr 2025 01:06:08 -0700 (PDT) Received: from gmonaco-thinkpadt14gen3.rmtit.csb ([185.107.56.42]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-39eaf44577dsm10267297f8f.94.2025.04.14.01.06.07 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 14 Apr 2025 01:06:08 -0700 (PDT) Message-ID: Subject: Re: [PATCH] timers: Exclude isolated cpus from timer migation From: Gabriele Monaco To: Frederic Weisbecker Cc: Thomas Gleixner , linux-kernel@vger.kernel.org, Waiman Long Date: Mon, 14 Apr 2025 10:06:06 +0200 In-Reply-To: References: <4fdc6582c828fbcd8c6ad202ed7ab560134d1fc3.camel@redhat.com> <56eae8396c5531b7a92a8e9e329ad68628e53729.camel@redhat.com> <1c60e19d1cebc09a8fd89f073c3dbec80c8ddbf1.camel@redhat.com> <75607f0eb5939bf1651ff2e6c3eda4df2b4f26f0.camel@redhat.com> <1047ba4c25cdf4c0098dac308bcddb4b8b671954.camel@redhat.com> Autocrypt: addr=gmonaco@redhat.com; prefer-encrypt=mutual; keydata=mDMEZuK5YxYJKwYBBAHaRw8BAQdAmJ3dM9Sz6/Hodu33Qrf8QH2bNeNbOikqYtxWFLVm0 1a0JEdhYnJpZWxlIE1vbmFjbyA8Z21vbmFjb0ByZWRoYXQuY29tPoiZBBMWCgBBFiEEysoR+AuB3R Zwp6j270psSVh4TfIFAmbiuWMCGwMFCQWjmoAFCwkIBwICIgIGFQoJCAsCBBYCAwECHgcCF4AACgk Q70psSVh4TfJzZgD/TXjnqCyqaZH/Y2w+YVbvm93WX2eqBqiVZ6VEjTuGNs8A/iPrKbzdWC7AicnK xyhmqeUWOzFx5P43S1E1dhsrLWgP Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.54.3 (3.54.3-1.fc41) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Sat, 2025-04-12 at 00:57 +0200, Frederic Weisbecker wrote: >=20 > If you want housekeeping CPUs to pull timers from isolated ones, then > you > need isolated CPUs to eventually be part of the hierarchy (be > "available"), > because they would need to propagate their global timers up to the > top. >=20 > If they propagate their global timers then they must play the whole > hierarchy > game and be ready to pull the timers from any other CPUs. >=20 > Because if they propagate their timers, they must also propagate > their > idle state to synchronize with the whole hierarchy and know if there > is > a non-idle housekeeping CPU to take care of their timers. And if they > propagate > their (non) idle state, the isolated CPUs also declare themselves as > available > to handle other's timers. >=20 > And working around that would be very nasty. >=20 Well, that's exactly what I was trying to do, thanks for pointing this out. I guess I won't go down that rabbit hole then. Thanks, Gabriele