From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1794504879; b=gCcnXnXy1PnXR7iNMLtlXsIY2K5pW5RRliysvgzg7grQQYEYpBLGn1OBnR+PyzU1N3aX 0NHvjzF5a6jAiYJib05yaFE3EmmExG0t/K+fS7hDRoyBx9BTZtEmSvgkNDRy82SuasHOl vZzqayTjwOKijjF6pSBBPQRezCJt8eInFc02lFA6i94mZGjqQ0hztZiDuvTpsNPgC93c7 cWTz0ZoHZ2aIiZHYDqcRZc73uUZnwgRRKHiAMYKfGgCvfMubEPh6ce9jJEtORP7CfM+LP 7RUn8VnyKkRUTZm57Uhlr3Y0Dfa8hgPIx+MycIS9KfCO9w4ZxH91ouwgCOe3DV2/HXA== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794504879; h=Received:DKIM-Signature:Date:Message-ID:From:To:Cc:Subject: In-Reply-To:References:MIME-Version:Content-Type: Content-Transfer-Encoding; bh=wzwyNnKIjrnozPoGZW9Td2OwtKGX1s/ksO11oNcMF2o=; b=WqPn9c5Lvex0HfVJKF/4eYXtziiVC8lmGOhxhdLnJAm/GkuoCoMyyNn+KTWRfA40QUFc mNeUwAQyIgUJZ0BvOyKVkLd5Cz+sO0nJbCqUuB7MlTtdHdBeK39rZtl2BJRFlUiPSqCuF RD2CrvojORFSFBeGzT/ZiYBIw/SL8uYT54HaNtEt6/j6p2MByYfdfr0TukdJomVew0chP rEIFNce6fRgvqQuAf+XYio59KZsq+nZ+blhUgEt+z2cki7CgqKkypbUbC+GKqIRMUuogQ DX3YrQWByWy+GakoKuCBY0tSl8XbOSR5RJgYvHhUnI+pd+hEbbqJKEB1fksM25ekJzg== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=e9WIuLfC; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 56A1D606F28E; Thu, 12 Nov 2026 17:34:39 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=e9WIuLfC Received: by smtp.kernel.org (Postfix) with ESMTPSA id F40D01F000C4; Thu, 12 Nov 2026 17:34:38 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1794504879; bh=wzwyNnKIjrnozPoGZW9Td2OwtKGX1s/ksO11oNcMF2o=; h=Date:From:To:Cc:Subject:In-Reply-To:References; b=e9WIuLfCLY6UYzQC0AA42ciW2KFC9WkpP+EIqHqlwQiFsRytgycgP/EvVDAFeGrC1 AQIFXlLOvVVkeLTx/+ccnK3WHMGDieHWouWOHaqvuMKG787t3dDcO+gN3/5oBcNtas 8R8UCZ+i+zfitn1xKmbdHKylkhNpjPFrxOSh+j2vS1Plw6cGJgltFKp6OW5GBZibkV niATL4pWrlnqYvDVwog9pZ9RkKxUqClOQM8CsG5AEOLcDumqpivEKpVTukrexY6MYe EhtmDbG8El02VnXXlUSjq3ePoFmm3k5BwxANyWCdWYiBKxhJVNCk3iQPAhGj/9GPpd YiyX5tu1guogw== Date: Thu, 12 Nov 2026 07:34:38 -1000 Message-ID: <7a17d1d32232abe85b559d61b5d2c536@kernel.org> From: Tejun Heo To: Tao Cui Cc: void@manifault.com, arighi@nvidia.com, changwoo@igalia.com, liwanwu@kylinos.cn, usama.arif@linux.dev, sched-ext@lists.linux.dev, linux-kernel@vger.kernel.org, bpf@vger.kernel.org, Tao Cui Subject: Re: [PATCH 6/6] sched_ext: Clear the built-in idle masks on CPU hotplug transitions In-Reply-To: <20261112130934.563321-7-cui.tao@linux.dev> References: <20261112130934.563321-1-cui.tao@linux.dev> <20261112130934.563321-7-cui.tao@linux.dev> X-Mailing-List: bpf@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 Content-Transfer-Encoding: 7bit Hello, Tao. On Thu, Nov 12, 2026 at 09:09:34PM +0800, Tao Cui wrote: > offline CPU as an idle candidate, and the built-in select_cpu path may > claim it once before the guard layers bounce the wakeup, costing a > failed pick and a bumped SCX_EV_SELECT_CPU_FALLBACK each time. This is > not the documented racy and self-correcting regime of the idle SMT > handling: the stale bit is a deterministic leftover, and read-only > kfunc consumers never trigger the claim-time self-correction. The failure mode is benign, and the patch doesn't address even what it describes. With a scheduler which implements the hotplug ops and only reads the idle mask, the offline CPU stays set in the mask for the whole offline window with the patch applied, the same as without it. Thanks. -- tejun