From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751729AbdEBWkK (ORCPT ); Tue, 2 May 2017 18:40:10 -0400 Received: from userp1040.oracle.com ([156.151.31.81]:45913 "EHLO userp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751148AbdEBWkH (ORCPT ); Tue, 2 May 2017 18:40:07 -0400 Subject: Re: [PATCH v8 1/5] x86: add simple udelay calibration To: Lu Baolu , 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: Boris Ostrovsky Message-ID: Date: Tue, 2 May 2017 18:38:39 -0400 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.8.0 MIME-Version: 1.0 In-Reply-To: <1490083293-3792-2-git-send-email-baolu.lu@linux.intel.com> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit X-Source-IP: aserv0022.oracle.com [141.146.126.234] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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()? -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