From patchwork Thu Dec 9 15:09:31 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: David Woodhouse X-Patchwork-Id: 12666719 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 3F04EC4321E for ; Thu, 9 Dec 2021 15:10:22 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S239541AbhLIPNy (ORCPT ); Thu, 9 Dec 2021 10:13:54 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:43042 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S239422AbhLIPNs (ORCPT ); Thu, 9 Dec 2021 10:13:48 -0500 Received: from desiato.infradead.org (desiato.infradead.org [IPv6:2001:8b0:10b:1:d65d:64ff:fe57:4e05]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A334AC061746; Thu, 9 Dec 2021 07:10:14 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=desiato.20200630; h=Sender:Content-Transfer-Encoding: Content-Type:MIME-Version:References:In-Reply-To:Message-Id:Date:Subject:Cc: To:From:Reply-To:Content-ID:Content-Description; bh=Tc77RILQLKEcS45J/6Ljdmr/xCkfDC7wsVb7jXcmkrE=; b=J7SxWrwQN1mpGSB2T7VAPAB0qb MR1kPAE+p4cJdQi8A86XWVmgfTCZt5RU38XZntPBm5I5JB1+7oCcTxKzl0ttBsrFocyvjiyw2CTC2 LMga9CFm7Bn6LsCg0Ra2Mzr0jQ6yUYGqP3i+vjw+Ikp1JTVM7TAITBC2RgHab+sVmKE/CWlB3Qqie ziZWG/ZUQfDXDt6+ofP9BS0n7MuVhKy3zCjpEipsuOd3fj+Tzb0wuipooIov2rtTRRcMpCF8vmVyP Mm7jnA1OyEFyzgGqu2P2JMbxWZ8xZEEIYQ5aPqrBBRJgn+zMifA0ypwJ3Lg/G/q3zwI/+F3dsdm6+ BrNoaBmA==; Received: from i7.infradead.org ([2001:8b0:10b:1:21e:67ff:fecb:7a92]) by desiato.infradead.org with esmtpsa (Exim 4.94.2 #2 (Red Hat Linux)) id 1mvL3J-000Now-Vy; Thu, 09 Dec 2021 15:09:46 +0000 Received: from dwoodhou by i7.infradead.org with local (Exim 4.94.2 #2 (Red Hat Linux)) id 1mvL3J-0000xz-JM; Thu, 09 Dec 2021 15:09:45 +0000 From: David Woodhouse To: Thomas Gleixner Cc: Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, "H. Peter Anvin" , Paolo Bonzini , "Paul E. McKenney" , linux-kernel@vger.kernel.org, kvm@vger.kernel.org, rcu@vger.kernel.org, mimoja@mimoja.de, hewenliang4@huawei.com, hushiyuan@huawei.com, luolongjun@huawei.com, hejingxian@huawei.com Subject: [PATCH 04/11] cpu/hotplug: Add dynamic parallel bringup states before CPUHP_BRINGUP_CPU Date: Thu, 9 Dec 2021 15:09:31 +0000 Message-Id: <20211209150938.3518-5-dwmw2@infradead.org> X-Mailer: git-send-email 2.31.1 In-Reply-To: <20211209150938.3518-1-dwmw2@infradead.org> References: <20211209150938.3518-1-dwmw2@infradead.org> MIME-Version: 1.0 Sender: David Woodhouse X-SRS-Rewrite: SMTP reverse-path rewritten from by desiato.infradead.org. See http://www.infradead.org/rpr.html 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 773c83730906..45c327538321 100644 --- a/include/linux/cpuhotplug.h +++ b/include/linux/cpuhotplug.h @@ -131,6 +131,8 @@ 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 192e43a87407..1a46eb57d8f7 100644 --- a/kernel/cpu.c +++ b/kernel/cpu.c @@ -1462,6 +1462,24 @@ 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) @@ -1829,6 +1847,10 @@ 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; } @@ -1853,14 +1875,15 @@ 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;