From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from desiato.infradead.org (desiato.infradead.org [90.155.92.199]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 0A18745198E; Fri, 25 Sep 2026 07:43:34 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=90.155.92.199 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790322217; cv=none; b=a+mHV2vpgZVXIDMOGOh+Caa9e8Yvuvc5O+JmY3DA/YKigw9v8OiRMmOwVxuC5frVoI8ny/IMDkGvqkucQh/S6O2ez1yI4s4c8lnoFxmZxZys1p8cfaoazLAENU7I50opXbFkuvK1JXUHJ9E6cylY3hiMV16vcTwbkSgGayxcX7Q= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790322217; c=relaxed/simple; bh=HmLFghI7T/rZIZJUKluSxFd5PCbOk8DZrf0mZqC6KAg=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=h1+z1DpEDsNp3nlSumKrddpxMcAdETmbI+3FpjYu4uxX5yXCAjx9p9M5CvVkgC6T6wbjpNR0nyWmuGYwcP8RnupEAU2k2XVO0eLNZasiONm4Bk5tp3JG2y7jBq80NgRY4oku7dSA/YK0xr2354Afgu9bUTrjfexsyBCtmTcd2kI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=infradead.org; spf=pass smtp.mailfrom=infradead.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b=MUvezfih; arc=none smtp.client-ip=90.155.92.199 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=infradead.org Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=infradead.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="MUvezfih" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=desiato.20200630; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=KgGrQ2Rb3/9aZ1fMAFWII3W+U6TCnA4h9tEdG5e23tg=; b=MUvezfih/DPOzLe6xL8tgJcc9f 54kuO/Hi4KW4rV/RFK3dL01oQtgbBHLNRugpxCSH0JbSibJsBec6QcFcYV4TWLCIxDSkek+0+Wx3K hONBAOxR7C201wHRUFI4vyP9k0JD+29j15gP+dwfrRT9wAdwOvEZsRfXQyW/utTeYKkyQj/PRh/mX 9iR220DJ6s8VATFvPPWfRkBkdGWfC0e5JCUOhjrefItQ6Bq8+2bGl+Cjwo5C5Y02NzAw5QAcWwlmN I/sKbhdxBkJKJQ4GOiYFDVPqyaHxWq2YcZ2RXiL1mU6PGdPpXu6xatB8I/SQyG/Kou+UP/V8+tiN4 nkh5FZKA==; Received: from 77-249-17-252.cable.dynamic.v4.ziggo.nl ([77.249.17.252] helo=noisy.programming.kicks-ass.net) by desiato.infradead.org with esmtpsa (Exim 4.99.2 #2 (Red Hat Linux)) id 1xA0aS-0000000GhUh-2wRB; Fri, 25 Sep 2026 07:43:16 +0000 Received: by noisy.programming.kicks-ass.net (Postfix, from userid 1000) id CA9D430070F; Fri, 25 Sep 2026 09:43:14 +0200 (CEST) Date: Fri, 25 Sep 2026 09:43:14 +0200 From: Peter Zijlstra To: Shrikanth Hegde Cc: linux-kernel@vger.kernel.org, mingo@kernel.org, juri.lelli@redhat.com, vincent.guittot@linaro.org, yury.norov@gmail.com, kprateek.nayak@amd.com, iii@linux.ibm.com, corbet@lwn.net, meted@linux.ibm.com, ynorov@nvidia.com, tglx@kernel.org, gregkh@linuxfoundation.org, pbonzini@redhat.com, seanjc@google.com, vschneid@redhat.com, huschle@linux.ibm.com, rostedt@goodmis.org, dietmar.eggemann@arm.com, maddy@linux.ibm.com, srikar@linux.ibm.com, hdanton@sina.com, chleroy@kernel.org, vineeth@bitbyteword.org, frederic@kernel.org, arighi@nvidia.com, pauld@redhat.com, christian.loehle@arm.com, tj@kernel.org, tommaso.cucinotta@gmail.com, maz@kernel.org, rafael@kernel.org, rdunlap@infradead.org, kernellwp@gmail.com, linux-doc@vger.kernel.org, jgross@suse.com, virtualization@lists.linux.dev, sunlightlinux@gmail.com Subject: Re: [PATCH v13 06/13] sched/core: Try to use a preferred CPU in is_cpu_allowed Message-ID: <20260925074314.GF4121339@noisy.programming.kicks-ass.net> References: <20260909135617.871006-1-sshegde@linux.ibm.com> <20260909135617.871006-7-sshegde@linux.ibm.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260909135617.871006-7-sshegde@linux.ibm.com> On Wed, Sep 09, 2026 at 07:26:10PM +0530, Shrikanth Hegde wrote: > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > index a689a0cea4eb..b4ef2e92d786 100644 > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -2504,6 +2504,23 @@ static inline bool rq_has_pinned_tasks(struct rq *rq) > return rq->nr_pinned; > } > > +static inline bool task_can_sched_on_preferred(int cpu, struct task_struct *p) (somehow those arguments feel backwards) > +{ > + if (cpu_preferred(cpu)) > + return false; FWIW, this reads very weird. task_can_sched_on_preferred() returning false when task is on a preferred cpu. The question really is more like: can we migrate to a preferred CPU, and in that context it makes more sense. No point in migrating if we are already on one. Perhaps a comment on top of the function can clarify? > + /* Only FAIR tasks honor preferred CPU state */ > + if (unlikely(p->sched_class != &fair_sched_class)) > + return false; > + > + /* Ignore preferred state if task affinity is changing */ > + if (unlikely(!cpumask_test_cpu(task_cpu(p), p->cpus_ptr))) > + return false; > + > + return cpumask_intersects_and(p->cpus_ptr, cpu_preferred_mask, > + task_cpu_possible_mask(p)); > +}