From nobody Sat Sep 13 17:01:21 2025 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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 0218AC6379F for ; Wed, 1 Feb 2023 20:45:16 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230080AbjBAUpN (ORCPT ); Wed, 1 Feb 2023 15:45:13 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:53698 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229957AbjBAUpJ (ORCPT ); Wed, 1 Feb 2023 15:45:09 -0500 Received: from mail-wr1-x42a.google.com (mail-wr1-x42a.google.com [IPv6:2a00:1450:4864:20::42a]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 2873178ACE for ; Wed, 1 Feb 2023 12:44:55 -0800 (PST) Received: by mail-wr1-x42a.google.com with SMTP id m7so18494526wru.8 for ; Wed, 01 Feb 2023 12:44:55 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=bytedance-com.20210112.gappssmtp.com; s=20210112; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:from:to:cc:subject:date :message-id:reply-to; bh=iTNF1JvfCDajsaqBdlIe78iIn+/3qna+HTWlbtJK4ls=; b=PHsc2s0l5yODha3GL0699EVouPw2t2VyZ/NpijjKErd/Wse0mkuoPmiTOTBFK5druj O+8z9IC64HBK0PtRhvS00L1CHOP2Tt1XQgtckGVJrZCTenGyOpEdLF2JkiQ5W6uThjvg tMwTIAehAFNjejO5Fr1XdrMjLCqVEk0WzwMrrB1yFj9MMznXnzgGoYBfY9Q/uxOzjYYW iEpO5m6XjptcngDjwzD6aUIAmWwlDi3xWVhjEBAqmAIBiPGHAO6Z+AQUXn6HQwvkOdfm I8kjD6IWRNSzffMbkewI0/3WzZrr5qqOUkRNV+5PWo7liabF2u7hWJKLTAXVYKwlCHV0 w+/Q== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=iTNF1JvfCDajsaqBdlIe78iIn+/3qna+HTWlbtJK4ls=; b=sSbDhwZVULgb0lnpZTIYRO3V4b+qwL3s4mW4O0qZmzz+jgZc5qnnY7y2j7bxLAX0DL MbkYgadzfdJRCOLRNOS1Bn/B+ZgjviLlOwqs4fyD6X5n4+0m5Tv71uFbu+i2HnzCuMRn o5kP5oou0nYGufa86RICLvCpXKkKdRCMCZHJTHMWOICLacQ3E+mceM+5YrC3IRZVwrqA NDoX2roaWMNuZ+0JMG/UKpt5PmlJSCTsbrJ7xAbG3zQY8ed4eZ5J6cyhVEsTPqcXSLZi YHuBIE06pYOmq2K6TK3obR2uGXNUymz884flqv1Pau8nHaQVJjiqeVkMl3aU6Mf+8IZh I8iA== X-Gm-Message-State: AO0yUKW1Y7mVJqb1QcdWjG4xWT9U2XaY3mbRnOR+PSqJn2uW4iTM+zpl +/LSjzEvVpbaIHiY2cPaGoIvcA== X-Google-Smtp-Source: AK7set9K2jZQ3dASQTukVtaV7ib8QH+uixLDVCS8g+33bcBHV6hPhsVaFGTs1vQxeonMHtYAgViYGg== X-Received: by 2002:a5d:560e:0:b0:2bf:cfb4:817c with SMTP id l14-20020a5d560e000000b002bfcfb4817cmr3484247wrv.35.1675284293632; Wed, 01 Feb 2023 12:44:53 -0800 (PST) Received: from usaari01.cust.communityfibre.co.uk ([2a02:6b6a:b566:0:7611:c340:3d8d:d46c]) by smtp.gmail.com with ESMTPSA id n15-20020a5d598f000000b002bdff778d87sm19993584wri.34.2023.02.01.12.44.52 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 01 Feb 2023 12:44:53 -0800 (PST) From: Usama Arif To: dwmw2@infradead.org, tglx@linutronix.de Cc: mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, hpa@zytor.com, x86@kernel.org, pbonzini@redhat.com, paulmck@kernel.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org, rcu@vger.kernel.org, mimoja@mimoja.de, hewenliang4@huawei.com, thomas.lendacky@amd.com, seanjc@google.com, pmenzel@molgen.mpg.de, fam.zheng@bytedance.com, punit.agrawal@bytedance.com, simon.evans@bytedance.com, liangma@liangbit.com, David Woodhouse , Usama Arif Subject: [PATCH 7/9] x86/smpboot: Send INIT/SIPI/SIPI to secondary CPUs in parallel Date: Wed, 1 Feb 2023 20:43:36 +0000 Message-Id: <20230201204338.1337562-8-usama.arif@bytedance.com> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20230201204338.1337562-1-usama.arif@bytedance.com> References: <20230201204338.1337562-1-usama.arif@bytedance.com> MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: David Woodhouse When the APs can find their own APIC ID without assistance, we can do the AP bringup in parallel. Register a CPUHP_BP_PARALLEL_DYN stage "x86/cpu:kick" which just calls do_boot_cpu() to deliver INIT/SIPI/SIPI to each AP in turn before the normal native_cpu_up() does the rest of the hand-holding. The APs will then take turns through the real mode code (which has its own bitlock for exclusion) until they make it to their own stack, then proceed through the first few lines of start_secondary() and execute these parts in parallel: start_secondary() -> cr4_init() -> (some 32-bit only stuff so not in the parallel cases) -> cpu_init_secondary() -> cpu_init_exception_handling() -> cpu_init() -> wait_for_master_cpu() At this point they wait for the BSP to set their bit in cpu_callout_mask (from do_wait_cpu_initialized()), and release them to continue through the rest of cpu_init() and beyond. This reduces the time taken for bringup on my 28-thread Haswell system from about 120ms to 80ms. On a socket 96-thread Skylake it takes the bringup time from 500ms to 100ms. There is more speedup to be had by doing the remaining parts in parallel too =E2=80=94 especially notify_cpu_starting() in which the AP takes itself through all the stages from CPUHP_BRINGUP_CPU to CPUHP_ONLINE. But those require careful auditing to ensure they are reentrant, before we can go that far. [Usama Arif: fixed rebase conflict] Signed-off-by: David Woodhouse Signed-off-by: Usama Arif --- arch/x86/kernel/smpboot.c | 19 ++++++++++++++++--- 1 file changed, 16 insertions(+), 3 deletions(-) diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c index 44e9f7ae5afc..060813411f85 100644 --- a/arch/x86/kernel/smpboot.c +++ b/arch/x86/kernel/smpboot.c @@ -1329,9 +1329,12 @@ int native_cpu_up(unsigned int cpu, struct task_stru= ct *tidle) { int ret; =20 - ret =3D do_cpu_up(cpu, tidle); - if (ret) - return ret; + /* If parallel AP bringup isn't enabled, perform the first steps now. */ + if (!do_parallel_bringup) { + ret =3D do_cpu_up(cpu, tidle); + if (ret) + return ret; + } =20 ret =3D do_wait_cpu_initialized(cpu); if (ret) @@ -1353,6 +1356,12 @@ int native_cpu_up(unsigned int cpu, struct task_stru= ct *tidle) return ret; } =20 +/* Bringup step one: Send INIT/SIPI to the target AP */ +static int native_cpu_kick(unsigned int cpu) +{ + return do_cpu_up(cpu, idle_thread_get(cpu)); +} + /** * arch_disable_smp_support() - disables SMP support for x86 at runtime */ @@ -1543,6 +1552,10 @@ void __init native_smp_prepare_cpus(unsigned int max= _cpus) boot_cpu_data.x86_vendor =3D=3D X86_VENDOR_AMD) do_parallel_bringup =3D false; =20 + if (do_parallel_bringup) + cpuhp_setup_state_nocalls(CPUHP_BP_PARALLEL_DYN, "x86/cpu:kick", + native_cpu_kick, NULL); + snp_set_wakeup_secondary_cpu(); } =20 --=20 2.25.1