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 29970C28B30 for ; Mon, 17 Mar 2025 11:31:27 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:Content-Transfer-Encoding: Content-Type:In-Reply-To:MIME-Version:Date:Message-ID:From:References:To: Subject:CC:Reply-To:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=tAmGDM/+7YlnQdB/9oOG+i2eP94QiP9D93TdqzjP8uQ=; b=ELybMKMBmHdMNFaHJFtBh8L6bO VbMsrok3bU9ykg3Xu/F6Q3Y8zoiX6rC7CjTNDrmW8L2yRoP9gGvp74cdQDm6Rzuy5GjRY/VWr2UcC vSKln+1gI+ot5FLbpNqESqpVGgVN7w7vXcVz8r7517LkhS3vFh64tlgQC/qoqslqHFfVkcsU9BV8n f/Xa5SAWYhgPK3kXGe0Q24qsB4olLdOS3ptuM0uB20AYf4ssm4qtWbU6ZkAaTDNBekgMJ80fF2y6C +YXQVW3fckcmoenyML0PYs0WqFTLWbl3MG6cdfox2Ajqju9yTt/G1wYxvpSZ7bJvYtPPLvuY5s3rB v+zM0kMw==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98 #2 (Red Hat Linux)) id 1tu8ge-00000002P77-1UOR; Mon, 17 Mar 2025 11:31:16 +0000 Received: from szxga08-in.huawei.com ([45.249.212.255]) by bombadil.infradead.org with esmtps (Exim 4.98 #2 (Red Hat Linux)) id 1tu8ev-00000002Oms-49yZ for linux-arm-kernel@lists.infradead.org; Mon, 17 Mar 2025 11:29:31 +0000 Received: from mail.maildlp.com (unknown [172.19.88.194]) by szxga08-in.huawei.com (SkyGuard) with ESMTP id 4ZGXmj58Ndz1d0LT; Mon, 17 Mar 2025 19:29:09 +0800 (CST) Received: from kwepemd200014.china.huawei.com (unknown [7.221.188.8]) by mail.maildlp.com (Postfix) with ESMTPS id B3002140360; Mon, 17 Mar 2025 19:29:20 +0800 (CST) Received: from [10.67.121.177] (10.67.121.177) by kwepemd200014.china.huawei.com (7.221.188.8) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.1748.10; Mon, 17 Mar 2025 19:29:19 +0800 CC: , , , , , , , , , , , , , , , , , , , , , , , , Subject: Re: [PATCH v12 2/4] arch_topology: Support SMT control for OF based system To: Dietmar Eggemann References: <20250311075143.61078-1-yangyicong@huawei.com> <20250311075143.61078-3-yangyicong@huawei.com> <2bd3aa0a-d700-46bf-81d1-a5fb0364d1e0@arm.com> From: Yicong Yang Message-ID: Date: Mon, 17 Mar 2025 19:29:19 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.5.1 MIME-Version: 1.0 In-Reply-To: <2bd3aa0a-d700-46bf-81d1-a5fb0364d1e0@arm.com> Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit X-Originating-IP: [10.67.121.177] X-ClientProxiedBy: dggems702-chm.china.huawei.com (10.3.19.179) To kwepemd200014.china.huawei.com (7.221.188.8) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20250317_042930_340473_76DB2B75 X-CRM114-Status: GOOD ( 14.39 ) 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: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 2025/3/17 17:56, Dietmar Eggemann wrote: > On 11/03/2025 08:51, Yicong Yang wrote: >> From: Yicong Yang >> >> On building the topology from the devicetree, we've already gotten the >> SMT thread number of each core. Update the largest SMT thread number >> and enable the SMT control by the end of topology parsing. >> >> The framework's SMT control provides two interface to the users [1] >> through /sys/devices/system/cpu/smt/control: >> 1) enable SMT by writing "on" and disable by "off" >> 2) enable SMT by writing max_thread_number or disable by writing 1 >> >> Both method support to completely disable/enable the SMT cores so both >> work correctly for symmetric SMT platform and asymmetric platform with >> non-SMT and one type SMT cores like: >> core A: 1 thread >> core B: X (X!=1) threads >> >> Note that for a theoretically possible multiple SMT-X (X>1) core >> platform the SMT control is also supported as expected but only >> by writing the "on/off" method. > > Here we still have a little misunderstanding. IMHO, even on such a > system 2) would work too. > yes but only by writing the max_thread_number. e.g. a system with SMT number of 1 (no SMT core), X, Y (Y > X), 1 works same as "off" and Y works same as "on", as you shown below. write X will be blocked by the CPU framework: estuary:/sys/devices/system/cpu/smt$ cat control off # emulated CPU 0-7,16-22 as SMT-2, CPU 8-11,24-27 as SMT-4 estuary:/sys/devices/system/cpu/smt$ cat ../online 0,2,4,6,8,12-16,18,20,22,24,28-31 estuary:/sys/devices/system/cpu/smt$ echo 2 > control bash: echo: write error: Invalid argument estuary:/sys/devices/system/cpu/smt$ echo 4 > control estuary:/sys/devices/system/cpu/smt$ cat ../online 0-31 so method 1) will always match the expectation to fully enable/disable the SMT on all cores, that's I mean here. But 2) won't work if user expected to write 2 to enable SMT-2 (I think it'll will work if we support CONFIG_SMT_NUM_THREADS_DYNAMIC on arm64 later). Thanks. > My qemu example with SMT-1, SMT-2 and SMT-4 in one system from your v11: > > # cat /proc/schedstat | grep -v "^v\|^t" | awk '{print $1" "$2" "$3}' > cpu0 0 0 > domain0 MC ff > cpu1 0 0 > domain0 MC ff > cpu2 0 0 > domain0 SMT 0c > domain1 MC ff > cpu3 0 0 > domain0 SMT 0c > domain1 MC ff > cpu4 0 0 > domain0 SMT f0 > domain1 MC ff > cpu5 0 0 > domain0 SMT f0 > domain1 MC ff > cpu6 0 0 > domain0 SMT f0 > domain1 MC ff > cpu7 0 0 > domain0 SMT f0 > domain1 MC ff > > # cat /proc/cpuinfo | grep ^processor > processor : 0 > processor : 1 > processor : 2 > processor : 3 > processor : 4 > processor : 5 > processor : 6 > processor : 7 > > # echo 1 > /sys/devices/system/cpu/smt/control > > # cat /proc/cpuinfo | grep ^processor > processor : 0 > processor : 1 > processor : 2 > processor : 4 > > # echo 4 > /sys/devices/system/cpu/smt/control > > # cat /proc/cpuinfo | grep ^processor > processor : 0 > processor : 1 > processor : 2 > processor : 3 > processor : 4 > processor : 5 > processor : 6 > processor : 7 > > Whats doesn't work is to echoing a '2' but that's not > 'max_thread_number' of the system. > > [...] > > . >