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 09164C282CD for ; Mon, 3 Mar 2025 14:07:11 +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=w4SBa9yC7XMiHqkPnEAYuhNs4OVKvUn63r+47d6m9cE=; b=ceDw3baYNSO2XnTiTg+hYNo3ds zem89M/b3iqUbBrjEfB5MTbZE29P0YoV7EsfZ7ke3UFx1J4sxaQh7c8xhnTQ49sg+QFKGd+BZTgRs BYzeWlQJtorNsn+p9LJxZ3ZDekCvlgF7KkJivUWjaiSWoehi6JCdebDE1Bt80KytKuVpCZUwQ4GGX D1Y9HxPnZgziEablaQppNx3KyXTSC6PkGPXcCy4+SWTAZ/iTB/wTAm8fspzSw8dEjmcLSYQOt3ju5 ybXkV5twjFg5/Lbxq9OsLvYkUHgGiig7cVbxJBXWUtRzngg4YbB9RU18wk7IcIU9VczBb5UqpFQAq Yq3R9wfQ==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98 #2 (Red Hat Linux)) id 1tp6Re-000000011cg-0Kd3; Mon, 03 Mar 2025 14:06:58 +0000 Received: from szxga05-in.huawei.com ([45.249.212.191]) by bombadil.infradead.org with esmtps (Exim 4.98 #2 (Red Hat Linux)) id 1tp60a-00000000xET-1LA5 for linux-arm-kernel@lists.infradead.org; Mon, 03 Mar 2025 13:39:02 +0000 Received: from mail.maildlp.com (unknown [172.19.88.163]) by szxga05-in.huawei.com (SkyGuard) with ESMTP id 4Z60D32kYsz1ltbN; Mon, 3 Mar 2025 21:34:43 +0800 (CST) Received: from kwepemd200014.china.huawei.com (unknown [7.221.188.8]) by mail.maildlp.com (Postfix) with ESMTPS id 6E45D18001B; Mon, 3 Mar 2025 21:38:53 +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 15.2.1258.34; Mon, 3 Mar 2025 21:38:52 +0800 CC: , , , , , , , , , , , , , , , , , , , , , , , , Subject: Re: [PATCH v11 1/4] cpu/SMT: Provide a default topology_is_primary_thread() To: Sudeep Holla References: <20250218141018.18082-1-yangyicong@huawei.com> <20250218141018.18082-2-yangyicong@huawei.com> From: Yicong Yang Message-ID: Date: Mon, 3 Mar 2025 21:38:51 +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: Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit X-Originating-IP: [10.67.121.177] X-ClientProxiedBy: dggems706-chm.china.huawei.com (10.3.19.183) 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-20250303_053900_800866_90A97ECB X-CRM114-Status: GOOD ( 23.11 ) 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 2025/2/28 21:54, Sudeep Holla wrote: > On Tue, Feb 18, 2025 at 10:10:15PM +0800, Yicong Yang wrote: >> From: Yicong Yang >> >> Currently if architectures want to support HOTPLUG_SMT they need to >> provide a topology_is_primary_thread() telling the framework which >> thread in the SMT cannot offline. However arm64 doesn't have a >> restriction on which thread in the SMT cannot offline, a simplest >> choice is that just make 1st thread as the "primary" thread. So >> just make this as the default implementation in the framework and >> let architectures like x86 that have special primary thread to >> override this function (which they've already done). >> >> There's no need to provide a stub function if !CONFIG_SMP or >> !CONFIG_HOTPLUG_SMT. In such case the testing CPU is already >> the 1st CPU in the SMT so it's always the primary thread. >> >> Reviewed-by: Jonathan Cameron >> Signed-off-by: Yicong Yang >> --- >> Pre questioned in v9 [1] whether this works on architectures not using >> CONFIG_GENERIC_ARCH_TOPOLOGY, See [2] for demonstration hacking on LoongArch >> VM and this also works. Architectures should use this on their own situation. >> [1] https://lore.kernel.org/linux-arm-kernel/427bd639-33c3-47e4-9e83-68c428eb1a7d@arm.com/ >> [2] https://lore.kernel.org/linux-arm-kernel/a5690fee-3019-f26c-8bad-1d95e388e877@huawei.com/ >> >> arch/powerpc/include/asm/topology.h | 1 + >> arch/x86/include/asm/topology.h | 2 +- >> include/linux/topology.h | 22 ++++++++++++++++++++++ >> 3 files changed, 24 insertions(+), 1 deletion(-) >> >> diff --git a/arch/powerpc/include/asm/topology.h b/arch/powerpc/include/asm/topology.h >> index 16bacfe8c7a2..da15b5efe807 100644 >> --- a/arch/powerpc/include/asm/topology.h >> +++ b/arch/powerpc/include/asm/topology.h >> @@ -152,6 +152,7 @@ static inline bool topology_is_primary_thread(unsigned int cpu) >> { >> return cpu == cpu_first_thread_sibling(cpu); >> } >> +#define topology_is_primary_thread topology_is_primary_thread >> >> static inline bool topology_smt_thread_allowed(unsigned int cpu) >> { >> diff --git a/arch/x86/include/asm/topology.h b/arch/x86/include/asm/topology.h >> index ec134b719144..6c79ee7c0957 100644 >> --- a/arch/x86/include/asm/topology.h >> +++ b/arch/x86/include/asm/topology.h >> @@ -229,11 +229,11 @@ static inline bool topology_is_primary_thread(unsigned int cpu) >> { >> return cpumask_test_cpu(cpu, cpu_primary_thread_mask); >> } >> +#define topology_is_primary_thread topology_is_primary_thread >> >> #else /* CONFIG_SMP */ >> static inline int topology_phys_to_logical_pkg(unsigned int pkg) { return 0; } >> static inline int topology_max_smt_threads(void) { return 1; } >> -static inline bool topology_is_primary_thread(unsigned int cpu) { return true; } >> static inline unsigned int topology_amd_nodes_per_pkg(void) { return 1; } >> #endif /* !CONFIG_SMP */ >> >> diff --git a/include/linux/topology.h b/include/linux/topology.h >> index 52f5850730b3..b3aba443c4eb 100644 >> --- a/include/linux/topology.h >> +++ b/include/linux/topology.h >> @@ -240,6 +240,28 @@ static inline const struct cpumask *cpu_smt_mask(int cpu) >> } >> #endif >> >> +#ifndef topology_is_primary_thread >> + >> +#define topology_is_primary_thread topology_is_primary_thread >> + >> +static inline bool topology_is_primary_thread(unsigned int cpu) >> +{ >> + /* >> + * On SMT hotplug the primary thread of the SMT won't be disabled. > > I may be misunderstanding the term "SMT hotplug" above. For me it is > comparable with logical CPU hotplug, so the above statement may be > misleading. IIUC, what you mean above is if SMT is disabled, the > primary thread will always remain enabled/active. Does that make sense > or am I missing something ? > I just the borrow the term from kconfig HOTPLUG_SMT here, but here the statement only involves the disable part, so maybe it'll be more accurate to use "SMT disable" rather than "SMT hotplug" here? Thanks.