Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
        id S1752516AbdGCDXz (ORCPT <rfc822;w@1wt.eu>);
        Sun, 2 Jul 2017 23:23:55 -0400
Received: from cn.fujitsu.com ([59.151.112.132]:36755 "EHLO
        heian.cn.fujitsu.com" rhost-flags-OK-FAIL-OK-FAIL) by vger.kernel.org
        with ESMTP id S1752292AbdGCDXy (ORCPT
        <rfc822;linux-kernel@vger.kernel.org>);
        Sun, 2 Jul 2017 23:23:54 -0400
X-IronPort-AV: E=Sophos;i="5.22,518,1449504000"; 
   d="scan'208";a="20763233"
Subject: Re: [PATCH v5 08/12] x86/ioapic: Refactor the delay logic in
 timer_irq_works()
To: Thomas Gleixner <tglx@linutronix.de>
References: <cover.1498795030.git.douly.fnst@cn.fujitsu.com>
 <3ce38e2076e32d1e323f0ef9d236937c1c251bc1.1498795030.git.douly.fnst@cn.fujitsu.com>
 <alpine.DEB.2.20.1707022111140.2296@nanos>
CC: <x86@kernel.org>, <linux-kernel@vger.kernel.org>,
        <xen-devel@lists.xenproject.org>, <mingo@kernel.org>, <hpa@zytor.com>,
        <ebiederm@xmission.com>, <bhe@redhat.com>,
        <boris.ostrovsky@oracle.com>, <peterz@infradead.org>,
        <izumi.taku@jp.fujitsu.com>
From: Dou Liyang <douly.fnst@cn.fujitsu.com>
Message-ID: <b73aa56d-2fb6-feaa-00a3-b1d7b04c1679@cn.fujitsu.com>
Date: Mon, 3 Jul 2017 11:23:46 +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: <alpine.DEB.2.20.1707022111140.2296@nanos>
Content-Type: text/plain; charset="windows-1252"; format=flowed
Content-Transfer-Encoding: 7bit
X-Originating-IP: [10.167.226.106]
X-yoursite-MailScanner-ID: 5419C47E98A6.AA7E7
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: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org
Content-Length: 1427
Lines: 78

Hi Thomas,

At 07/03/2017 03:15 AM, Thomas Gleixner wrote:
> On Fri, 30 Jun 2017, Dou Liyang wrote:
>> +static void __init delay_with_tsc(void)
>> +{
>> +	unsigned long long start, now;
>> +	unsigned long ticks = jiffies;
>
> Please make that
>
>        unsigned long end = jiffies + 4;
>
> ticks really means: number of ticks. But that variable is doing something
> different.

um, I see. Will use 'end' instead.

>
>> +	start = rdtsc();
>> +
>> +	/*
>> +	 * We don't know the TSC frequency yet, but waiting for
>> +	 * 40000000000/HZ TSC cycles is safe:
>> +	 * 4 GHz == 10 jiffies
>> +	 * 1 GHz == 40 jiffies
>> +	 */
>> +	do {
>> +		rep_nop();
>> +		now = rdtsc();
>> +	} while ((now - start) < 40000000000UL / HZ &&
>> +		time_before_eq(jiffies, ticks + 4));
>> +}
>> +
>> +static void __init delay_without_tsc(void)
>> +{
>> +	int band = 1;
>> +	unsigned long ticks = jiffies;
>
> Please sort variables in reverse fir tree order
>
> 	unsigned long end = jiffies + 4;
> 	int band = 1;
>

OK, I will.

>> +
>> +	/*
>> +	 * We don't know any frequency yet, but waiting for
>> +	 * 40940000000/HZ cycles is safe:
>> +	 * 4 GHz == 10 jiffies
>> +	 * 1 GHz == 40 jiffies
>> +	 * 1 << 1 + 1 << 2 +...+ 1 << 11 = 4094
>> +	 */
>> +	do {
>> +		__delay(((1 << band++) * 10000000UL) / HZ);
>
>   s/1/1U/
>

Got it!

Thanks,

	dou.


>> +	} while (band < 12 && time_before_eq(jiffies, ticks + 4));
>> +}
>
> Thanks,
>
> 	tglx
>
>
>