From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755181AbdEEFl2 (ORCPT ); Fri, 5 May 2017 01:41:28 -0400 Received: from mga02.intel.com ([134.134.136.20]:53008 "EHLO mga02.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751079AbdEEFl1 (ORCPT ); Fri, 5 May 2017 01:41:27 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.38,291,1491289200"; d="scan'208";a="82836716" Subject: Re: [PATCH v8 1/5] x86: add simple udelay calibration To: Boris Ostrovsky , Greg Kroah-Hartman , Ingo Molnar References: <1490083293-3792-1-git-send-email-baolu.lu@linux.intel.com> <1490083293-3792-2-git-send-email-baolu.lu@linux.intel.com> Cc: Mathias Nyman , tglx@linutronix.de, peterz@infradead.org, linux-usb@vger.kernel.org, x86@kernel.org, linux-kernel@vger.kernel.org, Juergen Gross , xen-devel From: Lu Baolu Message-ID: <590C1084.7010302@linux.intel.com> Date: Fri, 5 May 2017 13:41:24 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.5.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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? Best regards, Lu Baolu > > -boris > > >> Cc: Ingo Molnar >> Cc: x86@kernel.org >> Signed-off-by: Lu Baolu >> --- >> arch/x86/kernel/setup.c | 22 ++++++++++++++++++++++ >> 1 file changed, 22 insertions(+) >> >> diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c >> index 4bf0c89..e70204e 100644 >> --- a/arch/x86/kernel/setup.c >> +++ b/arch/x86/kernel/setup.c >> @@ -837,6 +837,26 @@ dump_kernel_offset(struct notifier_block *self, unsigned long v, void *p) >> return 0; >> } >> >> +static void __init simple_udelay_calibration(void) >> +{ >> + unsigned int tsc_khz, cpu_khz; >> + unsigned long lpj; >> + >> + if (!boot_cpu_has(X86_FEATURE_TSC)) >> + return; >> + >> + 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 >