From patchwork Mon May 8 19:43:46 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Thomas Gleixner X-Patchwork-Id: 13234911 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 D8843C7EE2A for ; Mon, 8 May 2023 19:44:32 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233766AbjEHTob (ORCPT ); Mon, 8 May 2023 15:44:31 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:57998 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233655AbjEHToL (ORCPT ); Mon, 8 May 2023 15:44:11 -0400 Received: from galois.linutronix.de (Galois.linutronix.de [IPv6:2a0a:51c0:0:12e:550::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 67CD472A4; Mon, 8 May 2023 12:43:48 -0700 (PDT) Message-ID: <20230508185217.898282342@linutronix.de> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1683575026; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: references:references; bh=WRyTY63fFKNT8NNe9pdrXSxP97ZO9fcfInZz6PguA8M=; b=1cHMH34GyxfIxkvmlBecr+5mzqthYk0E5c5P4+XqqcL8e6XurHWWxoOFIeJNtH/QSimVPW 18V4fky6NzTdKRpcATR0yTdNUZbSMxJNRORImkmezodXTP7pe74xPQQAr7BpbhkgTBLmJ9 9+OjV54jcwTxOTA+n9J3KUmsDNgl2gb3hdT1mCXG5keQW7p23s7uTtMRmJhNI8qHCATek2 VFYxci2MRuYhxjE+yAzrFzousZ3auxKM0KBHlEanvL+LGxBtvIkKatD++/+hdxq+0bTgJP Q8JQ6UU2zRO8a9/lotv6c8YTYGM7ip1GcZN4ZI6sLMyO//NiTtDVmoUIAZOoIQ== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1683575026; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: references:references; bh=WRyTY63fFKNT8NNe9pdrXSxP97ZO9fcfInZz6PguA8M=; b=a+XTx0gdMg20467/DY65JXjTt0K7JO0GQA4Eac40m+yQL/vp4DDGDsEbZstdM86jzLh2iO AyCWRRDCHHJEPTBg== From: Thomas Gleixner To: LKML Cc: x86@kernel.org, David Woodhouse , Andrew Cooper , Brian Gerst , Arjan van de Veen , Paolo Bonzini , Paul McKenney , Tom Lendacky , Sean Christopherson , Oleksandr Natalenko , Paul Menzel , "Guilherme G. Piccoli" , Piotr Gorski , Usama Arif , Juergen Gross , Boris Ostrovsky , xen-devel@lists.xenproject.org, Russell King , Arnd Bergmann , linux-arm-kernel@lists.infradead.org, Catalin Marinas , Will Deacon , Guo Ren , linux-csky@vger.kernel.org, Thomas Bogendoerfer , linux-mips@vger.kernel.org, "James E.J. Bottomley" , Helge Deller , linux-parisc@vger.kernel.org, Paul Walmsley , Palmer Dabbelt , linux-riscv@lists.infradead.org, Mark Rutland , Sabin Rapan , "Michael Kelley (LINUX)" Subject: [patch v3 12/36] [patch V2 12/38] x86/smpboot: Make TSC synchronization function call based References: <20230508181633.089804905@linutronix.de> MIME-Version: 1.0 Date: Mon, 8 May 2023 21:43:46 +0200 (CEST) Precedence: bulk List-ID: X-Mailing-List: linux-mips@vger.kernel.org From: Thomas Gleixner Spin-waiting on the control CPU until the AP reaches the TSC synchronization is just a waste especially in the case that there is no synchronization required. As the synchronization has to run with interrupts disabled the control CPU part can just be done from a SMP function call. The upcoming AP issues that call async only in the case that synchronization is required. Signed-off-by: Thomas Gleixner Tested-by: Michael Kelley --- arch/x86/include/asm/tsc.h | 2 -- arch/x86/kernel/smpboot.c | 20 +++----------------- arch/x86/kernel/tsc_sync.c | 36 +++++++++++------------------------- 3 files changed, 14 insertions(+), 44 deletions(-) --- --- a/arch/x86/include/asm/tsc.h +++ b/arch/x86/include/asm/tsc.h @@ -55,12 +55,10 @@ extern bool tsc_async_resets; #ifdef CONFIG_X86_TSC extern bool tsc_store_and_check_tsc_adjust(bool bootcpu); extern void tsc_verify_tsc_adjust(bool resume); -extern void check_tsc_sync_source(int cpu); extern void check_tsc_sync_target(void); #else static inline bool tsc_store_and_check_tsc_adjust(bool bootcpu) { return false; } static inline void tsc_verify_tsc_adjust(bool resume) { } -static inline void check_tsc_sync_source(int cpu) { } static inline void check_tsc_sync_target(void) { } #endif --- a/arch/x86/kernel/smpboot.c +++ b/arch/x86/kernel/smpboot.c @@ -278,11 +278,7 @@ static void notrace start_secondary(void /* Otherwise gcc will move up smp_processor_id() before cpu_init() */ barrier(); - /* - * Check TSC synchronization with the control CPU, which will do - * its part of this from wait_cpu_online(), making it an implicit - * synchronization point. - */ + /* Check TSC synchronization with the control CPU. */ check_tsc_sync_target(); /* @@ -1144,21 +1140,11 @@ static void wait_cpu_callin(unsigned int } /* - * Bringup step four: Synchronize the TSC and wait for the target AP - * to reach set_cpu_online() in start_secondary(). + * Bringup step four: Wait for the target AP to reach set_cpu_online() in + * start_secondary(). */ static void wait_cpu_online(unsigned int cpu) { - unsigned long flags; - - /* - * Check TSC synchronization with the AP (keep irqs disabled - * while doing so): - */ - local_irq_save(flags); - check_tsc_sync_source(cpu); - local_irq_restore(flags); - /* * Wait for the AP to mark itself online, so the core caller * can drop sparse_irq_lock. --- a/arch/x86/kernel/tsc_sync.c +++ b/arch/x86/kernel/tsc_sync.c @@ -245,7 +245,6 @@ bool tsc_store_and_check_tsc_adjust(bool */ static atomic_t start_count; static atomic_t stop_count; -static atomic_t skip_test; static atomic_t test_runs; /* @@ -344,21 +343,14 @@ static inline unsigned int loop_timeout( } /* - * Source CPU calls into this - it waits for the freshly booted - * target CPU to arrive and then starts the measurement: + * The freshly booted CPU initiates this via an async SMP function call. */ -void check_tsc_sync_source(int cpu) +static void check_tsc_sync_source(void *__cpu) { + unsigned int cpu = (unsigned long)__cpu; int cpus = 2; /* - * No need to check if we already know that the TSC is not - * synchronized or if we have no TSC. - */ - if (unsynchronized_tsc()) - return; - - /* * Set the maximum number of test runs to * 1 if the CPU does not provide the TSC_ADJUST MSR * 3 if the MSR is available, so the target can try to adjust @@ -368,16 +360,9 @@ void check_tsc_sync_source(int cpu) else atomic_set(&test_runs, 3); retry: - /* - * Wait for the target to start or to skip the test: - */ - while (atomic_read(&start_count) != cpus - 1) { - if (atomic_read(&skip_test) > 0) { - atomic_set(&skip_test, 0); - return; - } + /* Wait for the target to start. */ + while (atomic_read(&start_count) != cpus - 1) cpu_relax(); - } /* * Trigger the target to continue into the measurement too: @@ -397,14 +382,14 @@ void check_tsc_sync_source(int cpu) if (!nr_warps) { atomic_set(&test_runs, 0); - pr_debug("TSC synchronization [CPU#%d -> CPU#%d]: passed\n", + pr_debug("TSC synchronization [CPU#%d -> CPU#%u]: passed\n", smp_processor_id(), cpu); } else if (atomic_dec_and_test(&test_runs) || random_warps) { /* Force it to 0 if random warps brought us here */ atomic_set(&test_runs, 0); - pr_warn("TSC synchronization [CPU#%d -> CPU#%d]:\n", + pr_warn("TSC synchronization [CPU#%d -> CPU#%u]:\n", smp_processor_id(), cpu); pr_warn("Measured %Ld cycles TSC warp between CPUs, " "turning off TSC clock.\n", max_warp); @@ -457,11 +442,12 @@ void check_tsc_sync_target(void) * SoCs the TSC is frequency synchronized, but still the TSC ADJUST * register might have been wreckaged by the BIOS.. */ - if (tsc_store_and_check_tsc_adjust(false) || tsc_clocksource_reliable) { - atomic_inc(&skip_test); + if (tsc_store_and_check_tsc_adjust(false) || tsc_clocksource_reliable) return; - } + /* Kick the control CPU into the TSC synchronization function */ + smp_call_function_single(cpumask_first(cpu_online_mask), check_tsc_sync_source, + (unsigned long *)(unsigned long)cpu, 0); retry: /* * Register this CPU's participation and wait for the