Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Subject: Re: [PATCH v14 20/25] x86/tsc: calibrate tsc only once
To:     Thomas Gleixner <tglx@linutronix.de>
Cc:     peterz@infradead.org, Steven Sistare <steven.sistare@oracle.com>,
        Daniel Jordan <daniel.m.jordan@oracle.com>,
        linux@armlinux.org.uk, schwidefsky@de.ibm.com,
        Heiko Carstens <heiko.carstens@de.ibm.com>,
        John Stultz <john.stultz@linaro.org>, sboyd@codeaurora.org,
        x86@kernel.org, LKML <linux-kernel@vger.kernel.org>,
        mingo@redhat.com, hpa@zytor.com, douly.fnst@cn.fujitsu.com,
        prarit@redhat.com, feng.tang@intel.com,
        Petr Mladek <pmladek@suse.com>, gnomes@lxorguk.ukuu.org.uk,
        linux-s390@vger.kernel.org, boris.ostrovsky@oracle.com,
        jgross@suse.com, pbonzini@redhat.com
References: <20180718022211.6259-1-pasha.tatashin@oracle.com>
 <20180718022211.6259-21-pasha.tatashin@oracle.com>
 <20180719103340.GA2494@hirez.programming.kicks-ass.net>
 <alpine.DEB.2.21.1807191300150.1602@nanos.tec.linutronix.de>
 <4295075b-8a0f-1723-2e80-1bbd2f038846@oracle.com>
 <alpine.DEB.2.21.1807191817080.1693@nanos.tec.linutronix.de>
 <CAGM2reYpApca9v-2qpVbTGXGVWiEEL5mkEWzTAvXFiztmtkh1Q@mail.gmail.com>
 <CAGM2rebBN0v0epfTssM=ShiWZ4GTDaN_cgGWdKE4+k+jV6CxyA@mail.gmail.com>
 <alpine.DEB.2.21.1807192240260.1693@nanos.tec.linutronix.de>
From:   Pavel Tatashin <pasha.tatashin@oracle.com>
Message-ID: <ae3e5320-b389-e8af-2905-1ccc37953da3@oracle.com>
Date:   Thu, 19 Jul 2018 16:46:43 -0400
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101
 Thunderbird/52.9.1
MIME-Version: 1.0
In-Reply-To: <alpine.DEB.2.21.1807192240260.1693@nanos.tec.linutronix.de>
Content-Type: text/plain; charset=utf-8
Content-Language: en-US
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk


On 07/19/2018 04:44 PM, Thomas Gleixner wrote:
> On Thu, 19 Jul 2018, Pavel Tatashin wrote:
> 
>> On Thu, Jul 19, 2018 at 12:49 PM Pavel Tatashin
>> <pasha.tatashin@oracle.com> wrote:
>>>
>>>> So create two functions. native_...early..() and native....(). The early
>>>> one does not contain the hpet/pmtimer stuff and it replaces the ops.pointer
>>>> with the late one which contains all of it.
>>>
>>> Good idea. Actually, the late one will contain only hpet/pmtimer and I
>>> will set it only if tsc frequency was not determined only.
>>
>> If we determined tsc early in boot using one of the quick methods:
>> from cpuid/msr/quick_pit, can we assume that frequencies of all other
>> CPUs will be determined the same way? Or do we still have to fallback
>> to PIT/HPET/PMTIMER? I wondering if we support heterogeneous
>> multi-socket platforms with different CPUs, because that the only
>> platforms where I see such scenario is possible.
> 
> The frequency for secondary CPUs is usually taken from the boot CPU and the
> only reason why recalibration can happen is when the CPU does not have a
> constant frequency TSC.
> 
> For that case the quick PIT + hpet/pmtimer calibration bundle is
> required. So yes, the early calibration might work with quick PIT (those
> CPUs definitely do not have MSR/CPUID based calibration), but the
> recalibration might fail the quick PIT calibration for various reasons.

OK, good, I implemented with this in-mind. I will send out a new series shortly.

Thank you,
Pavel

> 
> Thanks,
> 
> 	tglx
>