linux-kernel - Re: [PATCH v5 08/12] x86/ioapic: Refactor the delay logic in timer_irq

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Message-ID: <b73aa56d-2fb6-feaa-00a3-b1d7b04c1679@cn.fujitsu.com>
Date:   Mon, 3 Jul 2017 11:23:46 +0800
From:   Dou Liyang <douly.fnst@...fujitsu.com>
To:     Thomas Gleixner <tglx@...utronix.de>
CC:     <x86@...nel.org>, <linux-kernel@...r.kernel.org>,
        <xen-devel@...ts.xenproject.org>, <mingo@...nel.org>,
        <hpa@...or.com>, <ebiederm@...ssion.com>, <bhe@...hat.com>,
        <boris.ostrovsky@...cle.com>, <peterz@...radead.org>,
        <izumi.taku@...fujitsu.com>
Subject: Re: [PATCH v5 08/12] x86/ioapic: Refactor the delay logic in
 timer_irq_works()

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
>
>
>