From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 26B2FC6FA82 for ; Tue, 20 Sep 2022 01:43:51 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:MIME-Version:Subject:In-Reply-To: Message-ID:Cc:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: References:List-Owner; bh=NXTf5QWQItW+vjo5kkL6gZ1dA0QcYaLFfdHwIwZH8zI=; b=HZs hXsNhR7ZYk/4dERIny2iwCPwGjkV/B+ja1Pg+Dy2sg7Csx9FciOnfDV22wxV9dh///vilREBDMRcJ JEQa8Wx7b181/2GM1ZGocQM2sxv6BfTEgtKSnMk+0qMPVasyCzuuMtWhvZgvvqM1teGW/impYlyv+ ksWS7hLTNnkgi4KkbotM2iN+UJiMre9YdzHORX/xN7HtwkijmiZ4IpYAWb0M10J73ro4HvRyObz0u sThlxTE4BWPBrDhP6a6qPSjkgZHr9f/NNKsYVRCyRsKVXyGVh4Zrji0Jt5D2qXc6Fjjq+czwKVoE7 Cag+guahsoCgRjdsN1lkZJMp3IwmSVA==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1oaSHm-00H5Hs-32; Tue, 20 Sep 2022 01:42:54 +0000 Received: from sender4-op-o18.zoho.com ([136.143.188.18]) by bombadil.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1oaSHi-00H5FS-7W for linux-arm-kernel@lists.infradead.org; Tue, 20 Sep 2022 01:42:51 +0000 ARC-Seal: i=1; a=rsa-sha256; t=1663638166; cv=none; d=zohomail.com; s=zohoarc; b=VoDwtU2y70N+3ILydhgRGZFuJ4iaGCgD1eKzW+Aw72FBSDupaAswQVlS2aAHsV4FghQmfiQMk0woCHbwP1JfFDE1HJ9+1LyKqfmbRSZiiqnVaP8wMkRWWf/2zEL38JLPi/LHoBpsx8vYRtzPniQTGIEaiCSl+AbB0WJBYv2tJrI= ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=zohomail.com; s=zohoarc; t=1663638166; h=Content-Type:Content-Transfer-Encoding:Cc:Date:From:MIME-Version:Message-ID:Subject:To; bh=FJLkkors9V0AAKGl56jsI5yxpgHzA0gcHyxLMgNKuaw=; b=NGk+5EnU3KbvdI720pNPGB0KBb+kkXGIlzgok3l+bQ3fzkOfZP8lldnvIgIHtKfGs3INv6l9DpnnSyPGDP/clgMFoa4jpIB/n5JZd67988gRVrOsXN/CEhbhD8mJ93LmgIpIxJ9C9MDT2c4GelxCT7evJJCTmui9D0IDfOgDCOM= ARC-Authentication-Results: i=1; mx.zohomail.com; dkim=pass header.i=linux.beauty; spf=pass smtp.mailfrom=me@linux.beauty; dmarc=pass header.from= DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; t=1663638166; s=zmail; d=linux.beauty; i=me@linux.beauty; h=Date:Date:From:From:To:To:Cc:Cc:Message-ID:In-Reply-To:Subject:Subject:MIME-Version:Content-Type:Content-Transfer-Encoding:Message-Id:Reply-To; bh=FJLkkors9V0AAKGl56jsI5yxpgHzA0gcHyxLMgNKuaw=; b=Mgg2A4qSO2/9Jxux1Losrvi2fcGukf0TpIlPS4a/JROylARizm7O3hD/KWq6DFI5 pHJwf3F2ir/d5nHnjj3gSPOwJ0rswQ6Jw6oEV/ORMlC7yebiYgZNtes1Pxpg+kO3wi3 BAlls9t9T3vOJt5p7KzoltcpTj0EOeka6XUd9SQE= Received: from mail.zoho.com by mx.zohomail.com with SMTP id 1663638164918877.1004596880902; Mon, 19 Sep 2022 18:42:44 -0700 (PDT) Date: Tue, 20 Sep 2022 03:42:44 +0200 From: Li Chen To: "Arnd Bergmann" Cc: "linux-arm-kernel" Message-ID: <183588fd5a7.1074ac6241209386.2442883306267550831@linux.beauty> In-Reply-To: Subject: Why GICD_ITARGETSR is not used by Linux MIME-Version: 1.0 Importance: Medium User-Agent: Zoho Mail X-Mailer: Zoho Mail X-Bad-Reply: In-Reply-To but no 'Re:' in Subject. X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20220919_184250_353148_D29698A9 X-CRM114-Status: GOOD ( 10.63 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org Hi Arnd, I noticed GIC has GICD_ITARGETSR to distribute IRQ to different CPUs, but currently, it is not used by Linux. There was a patchset from MTK people: http://archive.lwn.net:8080/linux-kernel/1606486531-25719-1-git-send-email-hanks.chen@mediatek.com/T/#t which implements GIC-level IRQ distributor using GICD_ITARGETSR, but it is not accepted because the maintainer thinks it will break existing codes and not provide benefits compared with the existing affinity mechanism. IIUC, Linux only relies on affinity/irqbalance to distribute IRQ instead of architecture-specific solutions like GIC's distributor. Maybe latency can somewhat get improved, but there is no benchmark yet. I have two questions here: 1. Now that Linux doesn't use GICD_ITARGETSR, where does it set CPU 0 to be the only IRQ distributor core? 2. Do you know any other reasons that GICD_ITARGETSR is not used by Linux? Regards, Li _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel