From patchwork Fri Jun 10 15:13:14 2016 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Jan Beulich X-Patchwork-Id: 9170005 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork.web.codeaurora.org (Postfix) with ESMTP id 722486048C for ; Fri, 10 Jun 2016 15:15:26 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 6674E27D13 for ; Fri, 10 Jun 2016 15:15:26 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 5A0C72833F; Fri, 10 Jun 2016 15:15:26 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-4.2 required=2.0 tests=BAYES_00, RCVD_IN_DNSWL_MED autolearn=ham version=3.3.1 Received: from lists.xenproject.org (lists.xenproject.org [192.237.175.120]) (using TLSv1.2 with cipher AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.wl.linuxfoundation.org (Postfix) with ESMTPS id C263627D13 for ; Fri, 10 Jun 2016 15:15:25 +0000 (UTC) Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.84_2) (envelope-from ) id 1bBO7e-0007vb-En; Fri, 10 Jun 2016 15:13:22 +0000 Received: from mail6.bemta5.messagelabs.com ([195.245.231.135]) by lists.xenproject.org with esmtp (Exim 4.84_2) (envelope-from ) id 1bBO7c-0007u3-Na for xen-devel@lists.xenproject.org; Fri, 10 Jun 2016 15:13:20 +0000 Received: from [85.158.139.211] by server-7.bemta-5.messagelabs.com id CE/AA-10476-019DA575; Fri, 10 Jun 2016 15:13:20 +0000 X-Brightmail-Tracker: H4sIAAAAAAAAA+NgFlrKIsWRWlGSWpSXmKPExsXS6fjDS5f/ZlS 4wa03HBbft0xmcmD0OPzhCksAYxRrZl5SfkUCa8btffuZC85aV+y6tIKtgfGXQRcjJ4eQQJ5E 59yzTCA2r4CdxPIFE1hAbAkBQ4l981exgdgsAqoSCw7/Ywex2QTUJdqebWftYuTgEBEwkDh3N KmLkYuDWaCbUWLHJog5wgJOEvce7WAGqeEVEJT4u0MYJMwMNH5P7zG2CYxcsxAys5BkIGwtiY e/brFA2NoSyxa+ZgYpZxaQllj+jwMi7CBxYN1VRlQlILa3RNPZs+wLGDlWMaoXpxaVpRbpWuo lFWWmZ5TkJmbm6BoamOrlphYXJ6an5iQmFesl5+duYgQGHwMQ7GBc2+p8iFGSg0lJlDdxflS4 EF9SfkplRmJxRnxRaU5q8SFGGQ4OJQneb9eBcoJFqempFWmZOcA4gElLcPAoifBa3QBK8xYXJ OYWZ6ZDpE4xKkqJ83KCJARAEhmleXBtsNi7xCgrJczLCHSIEE9BalFuZgmq/CtGcQ5GJWHe/y DbeTLzSuCmvwJazAS0ePmRcJDFJYkIKakGxvT4K47FlkW2C+/lSLsetmZ4+Hv2FhMdkdnTjta efa0yfQ7PuWxNMe3Qq2WRK1+4nJ/G/ojVxqczw/DuRxXzxW/2u+U+uuhnFd+5Yekj73UT1zXn ryyriFjm+aw8yi2r5Xpc5Z72W+oypy4Yq0lbxF+95MkfKRxb1uth/VvZcdo0Qf3wX6cOK7EUZ yQaajEXFScCANoAMPe4AgAA X-Env-Sender: JBeulich@suse.com X-Msg-Ref: server-9.tower-206.messagelabs.com!1465571596!44343777!1 X-Originating-IP: [137.65.248.74] X-SpamReason: No, hits=0.0 required=7.0 tests= X-StarScan-Received: X-StarScan-Version: 8.46; banners=-,-,- X-VirusChecked: Checked Received: (qmail 19977 invoked from network); 10 Jun 2016 15:13:18 -0000 Received: from prv-mh.provo.novell.com (HELO prv-mh.provo.novell.com) (137.65.248.74) by server-9.tower-206.messagelabs.com with DHE-RSA-AES256-GCM-SHA384 encrypted SMTP; 10 Jun 2016 15:13:18 -0000 Received: from INET-PRV-MTA by prv-mh.provo.novell.com with Novell_GroupWise; Fri, 10 Jun 2016 09:13:15 -0600 Message-Id: <575AF52A02000078000F406F@prv-mh.provo.novell.com> X-Mailer: Novell GroupWise Internet Agent 14.2.0 Date: Fri, 10 Jun 2016 09:13:14 -0600 From: "Jan Beulich" To: "xen-devel" Mime-Version: 1.0 Cc: Andrew Cooper , Dario Faggioli , Joao Martins Subject: [Xen-devel] [PATCH] x86/time: adjust local system time initialization X-BeenThere: xen-devel@lists.xen.org X-Mailman-Version: 2.1.18 Precedence: list List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Errors-To: xen-devel-bounces@lists.xen.org Sender: "Xen-devel" X-Virus-Scanned: ClamAV using ClamSMTP Using the bare return value from read_platform_stime() is not suitable when local_time_calibration() is going to use its fat path: Divergence of several dozen microseconds between NOW() return values on different CPUs results when platform and local time don't stay in close sync. Latch local and platform time on the CPU initiating AP bringup, such that the AP can use these values to seed its stime_local_stamp with as little of an error as possible. The boot CPU, otoh, can simply calculate the correct initial value (other CPUs could do so too with even greater accuracy than the approach being introduced, but that can work only if all CPUs' TSCs start ticking at the same time, which generally can't be assumed to be the case on multi-socket systems). This slightly defers init_percpu_time() (moved ahead by commit dd2658f966 ["x86/time: initialise time earlier during start_secondary()"]) in order to reduce as much as possible the gap between populating the stamps and consuming them. Signed-off-by: Jan Beulich x86/time: adjust local system time initialization Using the bare return value from read_platform_stime() is not suitable when local_time_calibration() is going to use its fat path: Divergence of several dozen microseconds between NOW() return values on different CPUs results when platform and local time don't stay in close sync. Latch local and platform time on the CPU initiating AP bringup, such that the AP can use these values to seed its stime_local_stamp with as little of an error as possible. The boot CPU, otoh, can simply calculate the correct initial value (other CPUs could do so too with even greater accuracy than the approach being introduced, but that can work only if all CPUs' TSCs start ticking at the same time, which generally can't be assumed to be the case on multi-socket systems). This slightly defers init_percpu_time() (moved ahead by commit dd2658f966 ["x86/time: initialise time earlier during start_secondary()"]) in order to reduce as much as possible the gap between populating the stamps and consuming them. Signed-off-by: Jan Beulich --- a/xen/arch/x86/smpboot.c +++ b/xen/arch/x86/smpboot.c @@ -328,12 +328,12 @@ void start_secondary(void *unused) percpu_traps_init(); - init_percpu_time(); - cpu_init(); smp_callin(); + init_percpu_time(); + setup_secondary_APIC_clock(); /* @@ -996,6 +996,8 @@ int __cpu_up(unsigned int cpu) if ( (ret = do_boot_cpu(apicid, cpu)) != 0 ) return ret; + time_latch_stamps(); + set_cpu_state(CPU_STATE_ONLINE); while ( !cpu_online(cpu) ) { --- a/xen/arch/x86/time.c +++ b/xen/arch/x86/time.c @@ -1328,21 +1328,51 @@ static void time_calibration(void *unuse &r, 1); } +static struct { + s_time_t local_stime, master_stime; +} ap_bringup_ref; + +void time_latch_stamps(void) { + unsigned long flags; + u64 tsc; + + local_irq_save(flags); + ap_bringup_ref.master_stime = read_platform_stime(); + tsc = rdtsc(); + local_irq_restore(flags); + + ap_bringup_ref.local_stime = get_s_time_fixed(tsc); +} + void init_percpu_time(void) { struct cpu_time *t = &this_cpu(cpu_time); unsigned long flags; + u64 tsc; s_time_t now; /* Initial estimate for TSC rate. */ t->tsc_scale = per_cpu(cpu_time, 0).tsc_scale; local_irq_save(flags); - t->local_tsc_stamp = rdtsc(); now = read_platform_stime(); + tsc = rdtsc(); local_irq_restore(flags); t->stime_master_stamp = now; + /* + * To avoid a discontinuity (TSC and platform clock can't be expected + * to be in perfect sync), initialization here needs to match up with + * local_time_calibration()'s decision whether to use its fast path. + */ + if ( boot_cpu_has(X86_FEATURE_CONSTANT_TSC) ) + { + if ( system_state < SYS_STATE_smp_boot ) + now = get_s_time_fixed(tsc); + else + now += ap_bringup_ref.local_stime - ap_bringup_ref.master_stime; + } + t->local_tsc_stamp = tsc; t->stime_local_stamp = now; } --- a/xen/include/asm-x86/time.h +++ b/xen/include/asm-x86/time.h @@ -40,6 +40,7 @@ int time_suspend(void); int time_resume(void); void init_percpu_time(void); +void time_latch_stamps(void); struct ioreq; int hwdom_pit_access(struct ioreq *ioreq); --- a/xen/arch/x86/smpboot.c +++ b/xen/arch/x86/smpboot.c @@ -328,12 +328,12 @@ void start_secondary(void *unused) percpu_traps_init(); - init_percpu_time(); - cpu_init(); smp_callin(); + init_percpu_time(); + setup_secondary_APIC_clock(); /* @@ -996,6 +996,8 @@ int __cpu_up(unsigned int cpu) if ( (ret = do_boot_cpu(apicid, cpu)) != 0 ) return ret; + time_latch_stamps(); + set_cpu_state(CPU_STATE_ONLINE); while ( !cpu_online(cpu) ) { --- a/xen/arch/x86/time.c +++ b/xen/arch/x86/time.c @@ -1328,21 +1328,51 @@ static void time_calibration(void *unuse &r, 1); } +static struct { + s_time_t local_stime, master_stime; +} ap_bringup_ref; + +void time_latch_stamps(void) { + unsigned long flags; + u64 tsc; + + local_irq_save(flags); + ap_bringup_ref.master_stime = read_platform_stime(); + tsc = rdtsc(); + local_irq_restore(flags); + + ap_bringup_ref.local_stime = get_s_time_fixed(tsc); +} + void init_percpu_time(void) { struct cpu_time *t = &this_cpu(cpu_time); unsigned long flags; + u64 tsc; s_time_t now; /* Initial estimate for TSC rate. */ t->tsc_scale = per_cpu(cpu_time, 0).tsc_scale; local_irq_save(flags); - t->local_tsc_stamp = rdtsc(); now = read_platform_stime(); + tsc = rdtsc(); local_irq_restore(flags); t->stime_master_stamp = now; + /* + * To avoid a discontinuity (TSC and platform clock can't be expected + * to be in perfect sync), initialization here needs to match up with + * local_time_calibration()'s decision whether to use its fast path. + */ + if ( boot_cpu_has(X86_FEATURE_CONSTANT_TSC) ) + { + if ( system_state < SYS_STATE_smp_boot ) + now = get_s_time_fixed(tsc); + else + now += ap_bringup_ref.local_stime - ap_bringup_ref.master_stime; + } + t->local_tsc_stamp = tsc; t->stime_local_stamp = now; } --- a/xen/include/asm-x86/time.h +++ b/xen/include/asm-x86/time.h @@ -40,6 +40,7 @@ int time_suspend(void); int time_resume(void); void init_percpu_time(void); +void time_latch_stamps(void); struct ioreq; int hwdom_pit_access(struct ioreq *ioreq);