From patchwork Wed Feb 1 20:43:32 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: Usama Arif X-Patchwork-Id: 13124977 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 0911CC636D4 for ; Wed, 1 Feb 2023 20:45:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231463AbjBAUph (ORCPT ); Wed, 1 Feb 2023 15:45:37 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:53474 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230246AbjBAUpW (ORCPT ); Wed, 1 Feb 2023 15:45:22 -0500 Received: from mail-wr1-x434.google.com (mail-wr1-x434.google.com [IPv6:2a00:1450:4864:20::434]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 3ADBB783EB for ; Wed, 1 Feb 2023 12:44:51 -0800 (PST) Received: by mail-wr1-x434.google.com with SMTP id d14so18492539wrr.9 for ; Wed, 01 Feb 2023 12:44:51 -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=D35a783y9+r4vRds/PMwj8fmKYL9Opm+FKXtqgXxLHg=; b=eF8Rk+MtnUKV+dEzht46DG3sSGDcWvQ+IioOradRjywouK3nVCjQwpj3Pr2GEwQsba 7tLkNcl3tQT+CsojvjzsmHXw3l5ju/hSDjM55geghkRVpzOcX64DsACf3gT/2f6tBq1v aR57e9OqJVLpNokFXvga1NUbihdw4wjpjf5RlKzKlJk8kcwPRTcI7hteq2tOGSP3JSdz lagaOVJTlIP6+d3zuFyuNZrTVYnYUJJG9+gb44942jTHDWCeqZ3hVcrv7et+Jd0yXjy4 T9U/Rk+fw81fCu0qbz7UvgD4bw0sBXqpupRoGdTndDVubTi0zk6EvndWP0ijiSZw+jB1 wjPQ== 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=D35a783y9+r4vRds/PMwj8fmKYL9Opm+FKXtqgXxLHg=; b=u8UG5SdEeXfyn0hNBfKpa+YJcH1GP+IENSLPeAv03T6Xjs2UYBRHAcGGmW9y5yOOIp h/LqV+NFRVyH1nHZdW+Dc74FpDNYvui5iL4Itg2ICiUNZxcDDEZOFQT8oypa40PLKobq S1gMT3YQ+ceE83deqjJhZGQT8TUP7c4W+pVuXgrBivC5VIHUQYjvEJKwW0eUuS/3s553 OtNQ8Du2jfh/uc80zYEULzbbPxGBRSbopkz0kQEpS7VR7dtvD8sv3Eoh1WNc3zif++DE zR+IfCYILsjsqvQ936y8E4ia9ZqvgAoiwyhf4mn572lrALlJb/cyTTCuLOJSVQNyrljk InVA== X-Gm-Message-State: AO0yUKU+5pIcJegKFAv2VGm7J1h4muiBGSpYfknGFdtwDa/rB3ZRykKv xJZO0+K0iWw+xGMDLS2n1KKr5w== X-Google-Smtp-Source: AK7set9dzcCBGGbRYGTZ36N8GwRkQfwAcCCzIZv/iDMDQ+lhYIt17VF6kTIoT2JY3rFwj7xy8NehwA== X-Received: by 2002:adf:f5ca:0:b0:2bf:d686:c873 with SMTP id k10-20020adff5ca000000b002bfd686c873mr123344wrp.28.1675284289627; Wed, 01 Feb 2023 12:44:49 -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.34.2023.02.01.12.44.48 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 01 Feb 2023 12:44:49 -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 Subject: [PATCH 3/9] cpu/hotplug: Add dynamic parallel bringup states before CPUHP_BRINGUP_CPU Date: Wed, 1 Feb 2023 20:43:32 +0000 Message-Id: <20230201204338.1337562-4-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 Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org From: David Woodhouse If the platform registers these states, bring all CPUs to each registered state in turn, before the final bringup to CPUHP_BRINGUP_CPU. This allows the architecture to parallelise the slow asynchronous tasks like sending INIT/SIPI and waiting for the AP to come to life. There is a subtlety here: even with an empty CPUHP_BP_PARALLEL_DYN step, this means that *all* CPUs are brought through the prepare states and to CPUHP_BP_PREPARE_DYN before any of them are taken to CPUHP_BRINGUP_CPU and then are allowed to run for themselves to CPUHP_ONLINE. So any combination of prepare/start calls which depend on A-B ordering for each CPU in turn, such as the X2APIC code which used to allocate a cluster mask 'just in case' and store it in a global variable in the prep stage, then potentially consume that preallocated structure from the AP and set the global pointer to NULL to be reallocated in CPUHP_X2APIC_PREPARE for the next CPU... would explode horribly. We believe that X2APIC was the only such case, for x86. But this is why it remains an architecture opt-in. For now. Note that the new parallel stages do *not* yet bring each AP to the CPUHP_BRINGUP_CPU state. The final loop in bringup_nonboot_cpus() is untouched, bringing each AP in turn from the final PARALLEL_DYN state (or all the way from CPUHP_OFFLINE) to CPUHP_BRINGUP_CPU and then waiting for that AP to do its own processing and reach CPUHP_ONLINE before releasing the next. Parallelising that part by bringing them all to CPUHP_BRINGUP_CPU and then waiting for them all is an exercise for the future. Signed-off-by: David Woodhouse --- include/linux/cpuhotplug.h | 2 ++ kernel/cpu.c | 27 +++++++++++++++++++++++++-- 2 files changed, 27 insertions(+), 2 deletions(-) diff --git a/include/linux/cpuhotplug.h b/include/linux/cpuhotplug.h index f61447913db9..3c08d9acc7b1 100644 --- a/include/linux/cpuhotplug.h +++ b/include/linux/cpuhotplug.h @@ -132,6 +132,8 @@ enum cpuhp_state { CPUHP_MIPS_SOC_PREPARE, CPUHP_BP_PREPARE_DYN, CPUHP_BP_PREPARE_DYN_END = CPUHP_BP_PREPARE_DYN + 20, + CPUHP_BP_PARALLEL_DYN, + CPUHP_BP_PARALLEL_DYN_END = CPUHP_BP_PARALLEL_DYN + 4, CPUHP_BRINGUP_CPU, /* diff --git a/kernel/cpu.c b/kernel/cpu.c index bbad5e375d3b..67e4db9f334b 100644 --- a/kernel/cpu.c +++ b/kernel/cpu.c @@ -1481,6 +1481,24 @@ int bringup_hibernate_cpu(unsigned int sleep_cpu) void bringup_nonboot_cpus(unsigned int setup_max_cpus) { unsigned int cpu; + int n = setup_max_cpus - num_online_cpus(); + + /* ∀ parallel pre-bringup state, bring N CPUs to it */ + if (n > 0) { + enum cpuhp_state st = CPUHP_BP_PARALLEL_DYN; + + while (st <= CPUHP_BP_PARALLEL_DYN_END && + cpuhp_hp_states[st].name) { + int i = n; + + for_each_present_cpu(cpu) { + cpu_up(cpu, st); + if (!--i) + break; + } + st++; + } + } for_each_present_cpu(cpu) { if (num_online_cpus() >= setup_max_cpus) @@ -1858,6 +1876,10 @@ static int cpuhp_reserve_state(enum cpuhp_state state) step = cpuhp_hp_states + CPUHP_BP_PREPARE_DYN; end = CPUHP_BP_PREPARE_DYN_END; break; + case CPUHP_BP_PARALLEL_DYN: + step = cpuhp_hp_states + CPUHP_BP_PARALLEL_DYN; + end = CPUHP_BP_PARALLEL_DYN_END; + break; default: return -EINVAL; } @@ -1882,14 +1904,15 @@ static int cpuhp_store_callbacks(enum cpuhp_state state, const char *name, /* * If name is NULL, then the state gets removed. * - * CPUHP_AP_ONLINE_DYN and CPUHP_BP_PREPARE_DYN are handed out on + * CPUHP_AP_ONLINE_DYN and CPUHP_BP_P*_DYN are handed out on * the first allocation from these dynamic ranges, so the removal * would trigger a new allocation and clear the wrong (already * empty) state, leaving the callbacks of the to be cleared state * dangling, which causes wreckage on the next hotplug operation. */ if (name && (state == CPUHP_AP_ONLINE_DYN || - state == CPUHP_BP_PREPARE_DYN)) { + state == CPUHP_BP_PREPARE_DYN || + state == CPUHP_BP_PARALLEL_DYN)) { ret = cpuhp_reserve_state(state); if (ret < 0) return ret;