linux-kernel - Re: [RFC PATCH 2/6] x86/apic: Construct a framework for setuping APIC mode as soon as possible

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Date:   Thu, 6 Apr 2017 10:21:10 +0800
From:   Dou Liyang <douly.fnst@...fujitsu.com>
To:     Thomas Gleixner <tglx@...utronix.de>
CC:     <x86@...nel.org>, <linux-kernel@...r.kernel.org>,
        <mingo@...nel.org>, <ebiederm@...ssion.com>, <bhe@...hat.com>,
        <hpa@...or.com>, <izumi.taku@...fujitsu.com>
Subject: Re: [RFC PATCH 2/6] x86/apic: Construct a framework for setuping APIC
 mode as soon as possible

Hi Thomas,

At 04/05/2017 07:46 PM, Thomas Gleixner wrote:
> On Wed, 29 Mar 2017, Dou Liyang wrote:
>
>> Now, there are two ways to setup local apic and io-apic in X86 arch:
>>   1. In an SMP-capable system, it will be done when preparing the
>> cpus in native_smp_prepare_boot_cpu().
>>   2. If UP_LATE_INIT is y, it will be done in smp_init()
>>
>> And, there are many switches in kernel which can determine the way of
>> APIC mode setup, as shown below:
>>
>>   1. kconfig :
>>      CONFIG_X86_64; CONFIG_X86_LOCAL_APIC; CONFIG_x86_IO_APIC
>>   2. kernel option: disable_apic; skip_ioapic_setup
>>   3. BIOS : boot_cpu_has(X86_FEATURE_APIC)
>>   4. MP table: smp_found_config
>>   5. ACPI: acpi_lapic; acpi_ioapic; nr_ioapic
>>
>> The setup is late which cause the dump-capture kernel hangs with 'notsc'
>> option in 1st kernel option. and the use of these switches is messily.
>>
>> Before make the APIC mode setup earlier, construct a framework first to
>> prepare for the work and make the logic clear.
>
> Calling that a framework is slightly exaggerated. It's a selector function
> for the interrupt delivery mode.
>

Yes, Selector is what I want.

To tell the truth, I've been looking for a word that can summarize this
patch for a long time. :)


>>  #ifdef CONFIG_X86_X2APIC
>> diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c
>> index f4fc949..bf4ccd0 100644
>> --- a/arch/x86/kernel/apic/apic.c
>> +++ b/arch/x86/kernel/apic/apic.c
>> @@ -1153,6 +1153,63 @@ void __init sync_Arb_IDs(void)
>>  			APIC_INT_LEVELTRIG | APIC_DM_INIT);
>>  }
>>
>> +enum apic_bsp_mode {
>> +	APIC_BSP_MODEL_PIC = 0,
>> +	APIC_BSP_MODEL_VIRTUAL_WIRE,
>> +	APIC_BSP_MODEL_SYMMETRIC_IO,
>> +	APIC_BSP_MODEL_COUNT
>> +};
>> +
>> +static int __init apic_bsp_mode_check(void)
>> +{
>> +
>> +	/* Check kernel option */
>> +	if (disable_apic) {
>> +		pr_info("APIC disabled by kernel option\n");
>
> kernel option is ambiguous. "APIC disabled via kernel command line" is telling
> clearly where this comes from.
>

Thanks, will modify in my next version.

>> +		return APIC_BSP_MODEL_PIC;
>> +	}
>> +	/* Check BOIS */
>> +#ifdef CONFIG_X86_64
>> +	/* On 64-bit, The APIC is integrated, So, must have APIC feature */
>> +	if (!boot_cpu_has(X86_FEATURE_APIC)) {
>> +		disable_apic = 1;
>> +		pr_info("Apic disabled by BIOS\n");
>
> Please use APIC consistently.

Oops, Yes.

>
>> +		return APIC_BSP_MODEL_PIC;
>> +	}
>> +#else
>> +	if (!boot_cpu_has(X86_FEATURE_APIC) &&
>> +		APIC_INTEGRATED(boot_cpu_apic_version)) {
>> +		pr_err("BIOS bug, local APIC #%d not detected!...\n",
>> +			boot_cpu_physical_apicid);
>
> Please make that
>
> 		pr_err(FW_BUG, "Local APIC %d not detected, force emulation",
> 		       boot_cpu_physical_apicid);
>
> and for consistency reasosns this should also set disable_apic to 1.
>
>> +		return APIC_BSP_MODEL_PIC;

Yes. I will.

>> +	}
>> +#endif
>> +	/*
>> +	 * Check MP table, if neither an integrated nor a separate chip
>> +	 * doesn't exist.
>> +	 */
>> +	if (!boot_cpu_has(X86_FEATURE_APIC) && !smp_found_config) {
>> +		pr_info("BOIS don't support APIC, and no SMP configuration.\n");
>
> s/BOIS/BIOS/
>
> and for consistency reasosns this should also set disable_apic to 1.
>

OK.

>
>> +		return APIC_BSP_MODEL_PIC;
>> +	}
>> +
>> +	/* Check MP table, ps: if the virtual wire has been setup */
>> +	if (!smp_found_config) {
>> +		disable_ioapic_support();
>> +
>> +		/* Check local APIC, if SMP_NO_CONFIG */
>> +		if (!acpi_lapic)
>> +			pr_info("SMP motherboard not detected\n");
>> +
>> +		return APIC_BSP_MODEL_VIRTUAL_WIRE;
>> +	}
>> +
>> +	/* Other checks of ACPI options will be done in each setup function */
>> +
>> +	return APIC_BSP_MODEL_SYMMETRIC_IO;
>> +}
>> +
>>  /*
>>   * Setup the through-local-APIC virtual wire mode.
>>   */
>> @@ -1202,6 +1259,22 @@ void apic_virture_wire_mode_setup(void)
>>  	apic_write(APIC_LVT1, value);
>>  }
>>
>> +/* init the interrupt routing model for the BSP */
>> +void __init init_bsp_APIC(void)
>> +{
>> +	switch (apic_bsp_mode_check()) {
>> +	case APIC_BSP_MODEL_PIC:
>> +		pr_info("Keep in PIC mode(8259)\n");
>> +		return;
>> +	case APIC_BSP_MODEL_VIRTUAL_WIRE:
>> +		pr_info("switch to virtual wire model.\n");
>
> Please consistently start sentences with upper case letters.

Yes, I will check all the sentences and comments again carefully.

Thanks,
	Liyang
>
> Thanks,
>
> 	tglx
>
>
>