Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751265AbdGMBjs (ORCPT ); Wed, 12 Jul 2017 21:39:48 -0400 Received: from cn.fujitsu.com ([59.151.112.132]:58435 "EHLO heian.cn.fujitsu.com" rhost-flags-OK-FAIL-OK-FAIL) by vger.kernel.org with ESMTP id S1750718AbdGMBjq (ORCPT ); Wed, 12 Jul 2017 21:39:46 -0400 X-IronPort-AV: E=Sophos;i="5.22,518,1449504000"; d="scan'208";a="21220499" Subject: Re: [PATCH v8 1/5] x86: add simple udelay calibration To: Lu Baolu , Boris Ostrovsky , Greg Kroah-Hartman , Ingo Molnar , Mathias Nyman , References: <1490083293-3792-1-git-send-email-baolu.lu@linux.intel.com> <1490083293-3792-2-git-send-email-baolu.lu@linux.intel.com> <590C1084.7010302@linux.intel.com> <5966CA3F.2030402@linux.intel.com> CC: , , , , Juergen Gross , xen-devel From: Dou Liyang Message-ID: <4b423b45-3b83-ead5-1205-a004d13dac77@cn.fujitsu.com> Date: Thu, 13 Jul 2017 09:39:38 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.4.0 MIME-Version: 1.0 In-Reply-To: <5966CA3F.2030402@linux.intel.com> Content-Type: text/plain; charset="windows-1252"; format=flowed Content-Transfer-Encoding: 7bit X-Originating-IP: [10.167.226.106] X-yoursite-MailScanner-ID: 484DB46B4C96.AF2F6 X-yoursite-MailScanner: Found to be clean X-yoursite-MailScanner-From: douly.fnst@cn.fujitsu.com Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3725 Lines: 129 Hi, Lu At 07/13/2017 09:17 AM, Lu Baolu wrote: > Hi, > > On 07/12/2017 04:02 PM, Dou Liyang wrote: >> Hi, Lu >> >> At 05/05/2017 08:50 PM, Boris Ostrovsky wrote: >>> On 05/05/2017 01:41 AM, Lu Baolu wrote: >>>> Hi, >>>> >>>> On 05/03/2017 06:38 AM, Boris Ostrovsky wrote: >>>>> On 03/21/2017 04:01 AM, Lu Baolu wrote: >>>>>> Add a simple udelay calibration in x86 architecture-specific >>>>>> boot-time initializations. This will get a workable estimate >>>>>> for loops_per_jiffy. Hence, udelay() could be used after this >>>>>> initialization. >>>>> This breaks Xen PV guests since at this point, and until >>>>> x86_init.paging.pagetable_init() which is when pvclock_vcpu_time_info is >>>>> mapped, they cannot access pvclock. >>>>> >>>>> Is it reasonable to do this before tsc_init() is called? (The failure >>>>> has nothing to do with tsc_init(), really --- it's just that it is >>>>> called late enough that Xen PV guests get properly initialized.) If it >>>>> is, would it be possible to move simple_udelay_calibration() after >>>>> x86_init.paging.pagetable_init()? >>>> This is currently only used for bare metal. How about by-pass it >>>> for Xen PV guests? >>> >>> It is fixed this for Xen PV guests now (in the sense that we don't crash >>> anymore) but my question is still whether this is not too early. Besides >>> tsc_init() (which might not be important here), at the time when >>> simple_udelay_calibration() is invoked we haven't yet called: >>> * kvmclock_init(), which sets calibration routines for KVM >>> * init_hypervisor_platform(), which sets calibration routines for vmware >>> and Xen HVM >>> * x86_init.paging.pagetable_init(), which sets calibration routines for >>> Xen PV >>> >> >> I guess these may have been missed. >> >> Do you have any comments about these? >> > > The patch will be available in 4.13-rc1. Yes, I have seen it in the upstream. Firstly, I also met this problem want to call udelay() earlier than *loops_per_jiffy* setup like you[1]. So I am very interesting in this patch. ;) I am also confused about the questions which Boris asked: whether do the CPU and TSC calibration too early just for using udelay()? this design broke our interface of x86_paltform.calibrate_cpu/tsc. And I also have a question below. [...] >>>>>> >>>>>> +static void __init simple_udelay_calibration(void) >>>>>> +{ >>>>>> + unsigned int tsc_khz, cpu_khz; >>>>>> + unsigned long lpj; >>>>>> + >>>>>> + if (!boot_cpu_has(X86_FEATURE_TSC)) >>>>>> + return; if we don't have the TSC feature in booting CPU and it returns here, can we use udelay() correctly like before? [1] https://lkml.org/lkml/2017/7/3/276 Thanks, dou. >> Thanks, >> >> dou. >> >>>>>> + >>>>>> + cpu_khz = x86_platform.calibrate_cpu(); >>>>>> + tsc_khz = x86_platform.calibrate_tsc(); >>>>>> + >>>>>> + tsc_khz = tsc_khz ? : cpu_khz; >>>>>> + if (!tsc_khz) >>>>>> + return; >>>>>> + >>>>>> + lpj = tsc_khz * 1000; >>>>>> + do_div(lpj, HZ); >>>>>> + loops_per_jiffy = lpj; >>>>>> +} >>>>>> + >>>>>> /* >>>>>> * Determine if we were loaded by an EFI loader. If so, then we have also been >>>>>> * passed the efi memmap, systab, etc., so we should use these data structures >>>>>> @@ -985,6 +1005,8 @@ void __init setup_arch(char **cmdline_p) >>>>>> */ >>>>>> x86_configure_nx(); >>>>>> >>>>>> + simple_udelay_calibration(); >>>>>> + >>>>>> parse_early_param(); >>>>>> >>>>>> #ifdef CONFIG_MEMORY_HOTPLUG >>> >>> >>> >>> >> >> >> -- >> To unsubscribe from this list: send the line "unsubscribe linux-usb" in >> the body of a message to majordomo@vger.kernel.org >> More majordomo info at http://vger.kernel.org/majordomo-info.html >> > > > >