From patchwork Thu Mar 17 16:12:13 2016 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Joao Martins X-Patchwork-Id: 8612871 Return-Path: X-Original-To: patchwork-xen-devel@patchwork.kernel.org Delivered-To: patchwork-parsemail@patchwork1.web.kernel.org Received: from mail.kernel.org (mail.kernel.org [198.145.29.136]) by patchwork1.web.kernel.org (Postfix) with ESMTP id 7BAF29F44D for ; Thu, 17 Mar 2016 16:16:44 +0000 (UTC) Received: from mail.kernel.org (localhost [127.0.0.1]) by mail.kernel.org (Postfix) with ESMTP id 8651920304 for ; Thu, 17 Mar 2016 16:16:43 +0000 (UTC) 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.kernel.org (Postfix) with ESMTPS id 85F4E202EC for ; Thu, 17 Mar 2016 16:16:42 +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 1agaYw-0004UG-K4; Thu, 17 Mar 2016 16:14:14 +0000 Received: from mail6.bemta5.messagelabs.com ([195.245.231.135]) by lists.xenproject.org with esmtp (Exim 4.84_2) (envelope-from ) id 1agaYv-0004Tj-AV for xen-devel@lists.xen.org; Thu, 17 Mar 2016 16:14:13 +0000 Received: from [85.158.139.211] by server-1.bemta-5.messagelabs.com id 0C/86-29419-4D7DAE65; Thu, 17 Mar 2016 16:14:12 +0000 X-Env-Sender: joao.m.martins@oracle.com X-Msg-Ref: server-7.tower-206.messagelabs.com!1458231249!29568504!1 X-Originating-IP: [141.146.126.69] X-SpamReason: No, hits=0.0 required=7.0 tests=sa_preprocessor: VHJ1c3RlZCBJUDogMTQxLjE0Ni4xMjYuNjkgPT4gMjc3MjE4\n X-StarScan-Received: X-StarScan-Version: 8.11; banners=-,-,- X-VirusChecked: Checked Received: (qmail 59173 invoked from network); 17 Mar 2016 16:14:11 -0000 Received: from aserp1040.oracle.com (HELO aserp1040.oracle.com) (141.146.126.69) by server-7.tower-206.messagelabs.com with DHE-RSA-AES256-GCM-SHA384 encrypted SMTP; 17 Mar 2016 16:14:11 -0000 Received: from aserv0021.oracle.com (aserv0021.oracle.com [141.146.126.233]) by aserp1040.oracle.com (Sentrion-MTA-4.3.2/Sentrion-MTA-4.3.2) with ESMTP id u2HGE8gc012500 (version=TLSv1 cipher=DHE-RSA-AES256-SHA bits=256 verify=OK); Thu, 17 Mar 2016 16:14:08 GMT Received: from userv0121.oracle.com (userv0121.oracle.com [156.151.31.72]) by aserv0021.oracle.com (8.13.8/8.13.8) with ESMTP id u2HGE7HP007350 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=FAIL); Thu, 17 Mar 2016 16:14:07 GMT Received: from abhmp0006.oracle.com (abhmp0006.oracle.com [141.146.116.12]) by userv0121.oracle.com (8.13.8/8.13.8) with ESMTP id u2HGE6FT005625; Thu, 17 Mar 2016 16:14:07 GMT Received: from localhost.localdomain (/89.181.14.119) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Thu, 17 Mar 2016 09:12:35 -0700 MIME-Version: 1.0 Message-ID: <1458231136-13457-3-git-send-email-joao.m.martins@oracle.com> Date: Thu, 17 Mar 2016 09:12:13 -0700 (PDT) From: Joao Martins To: xen-devel@lists.xen.org References: <1458231136-13457-1-git-send-email-joao.m.martins@oracle.com> In-Reply-To: <1458231136-13457-1-git-send-email-joao.m.martins@oracle.com> X-Mailer: git-send-email 2.1.4 X-Source-IP: aserv0021.oracle.com [141.146.126.233] Cc: Andrew Cooper , Joao Martins , Keir Fraser , Jan Beulich Subject: [Xen-devel] [PATCH 2/5] x86/time: implement tsc as clocksource 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-Spam-Status: No, score=-1.9 required=5.0 tests=BAYES_00, UNPARSEABLE_RELAY autolearn=unavailable version=3.3.1 X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on mail.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP Introduce support for using TSC as platform time which is the highest resolution time and most performant to get (~20 nsecs). Though there are also several problems associated with its usage, and there isn't a complete (and architecturally defined) guarantee that all machines will provide reliable and monotonic TSC across all CPUs, on different sockets and different P/C states. I believe Intel to be the only that can guarantee that. For this reason it's set with less priority when compared to HPET unless adminstrator changes "clocksource" boot option to "tsc". Upon initializing it, we also check for time warps and appropriate CPU features i.e. TSC_RELIABLE, CONSTANT_TSC and NONSTOP_TSC. And in case none of these conditions are met, we fail in order to fallback to the next available clocksource. It is also worth noting that with clocksource=tsc there isn't any need to synchronise with another clocksource, and I could verify that great portion the time skew was eliminated and seeing much less time warps happening. With HPET I observed ~500 warps in the period of 1h of around 27 us, and with TSC down to 50 warps in the same period having each warp < 100 ns. The warps still exist though but are only related to cross CPU calibration (being how much it takes to rendezvous with master), in which a later patch in this series aims to solve. Signed-off-by: Joao Martins --- Cc: Keir Fraser Cc: Jan Beulich Cc: Andrew Cooper Changes since RFC: - Spelling fixes in the commit message. - Remove unused clocksource_is_tsc variable and introduce it instead on the patch that uses it. - Move plt_tsc from second to last in the available clocksources. --- xen/arch/x86/time.c | 62 +++++++++++++++++++++++++++++++++++++++++++++++++++-- 1 file changed, 60 insertions(+), 2 deletions(-) diff --git a/xen/arch/x86/time.c b/xen/arch/x86/time.c index 687e39b..1311c58 100644 --- a/xen/arch/x86/time.c +++ b/xen/arch/x86/time.c @@ -432,6 +432,63 @@ uint64_t ns_to_acpi_pm_tick(uint64_t ns) } /************************************************************ + * PLATFORM TIMER 4: TSC + */ +static u64 tsc_freq; +static unsigned long tsc_max_warp; +static void tsc_check_reliability(void); + +static int __init init_tsctimer(struct platform_timesource *pts) +{ + bool_t tsc_reliable = 0; + + tsc_check_reliability(); + + if ( tsc_max_warp > 0 ) + { + tsc_reliable = 0; + printk("TSC: didn't passed warp test\n"); + } + else if ( boot_cpu_has(X86_FEATURE_TSC_RELIABLE) || + ( boot_cpu_has(X86_FEATURE_CONSTANT_TSC) && + boot_cpu_has(X86_FEATURE_NONSTOP_TSC) ) ) + { + tsc_reliable = 1; + } + else if ( boot_cpu_has(X86_FEATURE_CONSTANT_TSC) ) + { + tsc_reliable = (max_cstate <= 2); + + if (tsc_reliable) + printk("TSC: no deep Cstates, deemed reliable\n"); + else + printk("TSC: deep Cstates possible, so not reliable\n"); + } + + pts->frequency = tsc_freq; + return tsc_reliable; +} + +static u64 read_tsc(void) +{ + return rdtsc(); +} + +static void resume_tsctimer(struct platform_timesource *pts) +{ +} + +static struct platform_timesource __initdata plt_tsc = +{ + .id = "tsc", + .name = "TSC", + .read_counter = read_tsc, + .counter_bits = 64, + .init = init_tsctimer, + .resume = resume_tsctimer, +}; + +/************************************************************ * GENERIC PLATFORM TIMER INFRASTRUCTURE */ @@ -536,7 +593,7 @@ static void resume_platform_timer(void) static void __init init_platform_timer(void) { static struct platform_timesource * __initdata plt_timers[] = { - &plt_hpet, &plt_pmtimer, &plt_pit + &plt_hpet, &plt_pmtimer, &plt_pit, &plt_tsc }; struct platform_timesource *pts = NULL; @@ -1181,7 +1238,7 @@ static void check_tsc_warp(unsigned long tsc_khz, unsigned long *max_warp) } } -static unsigned long tsc_max_warp, tsc_check_count; +static unsigned long tsc_check_count; static cpumask_t tsc_check_cpumask; static void tsc_check_slave(void *unused) @@ -1465,6 +1522,7 @@ void __init early_time_init(void) struct cpu_time *t = &this_cpu(cpu_time); u64 tmp = init_pit_and_calibrate_tsc(); + tsc_freq = tmp; set_time_scale(&t->tsc_scale, tmp); t->local_tsc_stamp = boot_tsc_stamp;