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Wed, 11 Nov 2026 12:20:44 +0000 From: Fernand Sieber To: CC: , , , , , , , , , , , , , , , , , , , , , , , , , , , , , Subject: Re: [PATCH v2 0/4] sched/fair: cpu.max.runtime and idle refill for CPU credits Date: Wed, 11 Nov 2026 14:20:39 +0200 Message-ID: <20261111122039.47687-1-sieberf@amazon.com> X-Mailer: git-send-email 2.47.3 In-Reply-To: <3bdd435fd868ed7ca7ea9061e5966b7b@kernel.org> References: <3bdd435fd868ed7ca7ea9061e5966b7b@kernel.org> X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" X-ClientProxiedBy: EX19D031UWA001.ant.amazon.com (10.13.139.88) To EX19D001UWA001.ant.amazon.com (10.13.138.214) Content-Transfer-Encoding: 7bit Hi Tejun, Thank you for your prompt feedback. On Tue, 10 Nov 2026 10:10:41 -1000, Tejun Heo wrote: > If a burstable budget is something useful to add to fair, can you do > that first and separately? It should be able to stand on its own. That works for me as a starting point. I will resend just patches 1 and 2 as v3. > Seamlessly switching tasks between the classes in partial mode has a lot > of other integration problems beyond this one > [...] > The sched_ext part can just be a feature of your own BPF scheduler, > which you seem to be using already. There, the credit level is just > state in your BPF maps which your userspace can read and set, so the > maximalist version can wait until the need is proven. If you want a > handover between your scheduler and fair, that can be done from > userspace. The minimal viable bar for us is to never lose track of CPU credits. With patches 1 and 2, the userspace handover you suggest covers the planned transitions: on roll out and roll back, userspace reads cpu.max.runtime before the switch and writes it back after. The one case it cannot cover is an unplanned exit, a BPF scheduler erroring out or killed by the watchdog and falling back to fair, where there is no window for userspace to hand the level back. Thanks, Fernand Amazon Development Centre (South Africa) (Proprietary) Limited 29 Gogosoa Street, Observatory, Cape Town, Western Cape, 7925, South Africa Registration Number: 2004 / 034463 / 07