linux-kernel - Re: [RESEND PATCH 1/3] x86/apic: Set up through LAPIC on boot CPU's LINT0 if ioapic is disabled

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Message-ID: <20180117092743.GL10882@localhost.localdomain>
Date:   Wed, 17 Jan 2018 17:27:43 +0800
From:   Baoquan He <bhe@...hat.com>
To:     linux-kernel@...r.kernel.org, ebiederm@...ssion.com
Cc:     mingo@...hat.com, tglx@...utronix.de, hpa@...or.com,
        x86@...nel.org, douly.fnst@...fujitsu.com, rostedt@...dmis.org,
        jgross@...e.com, peterz@...radead.org, uobergfe@...hat.com,
        joro@...tes.org
Subject: Re: [RESEND PATCH 1/3] x86/apic: Set up through LAPIC on boot CPU's
 LINT0 if ioapic is disabled

CC Eric

On 01/05/18 at 12:37pm, Baoquan He wrote:
> Kdump kernel will become very slow if 'noapic' is specified in kernel
> command line. Normal kernel doesn't have this issue.
> 
> This is because the legacy irq mode is disabled in crashed kernel before
> jump jump to kdump kernel since commit 522e664644 ("x86/apic: Disable I/O
> APIC before shutdown of the local APIC") is merged. While in normal kernel,
> the legacy irq mode has been set in BIOS.
> 
> So we need set the delivery mode AS ExtINT for LVT0 of boot CPU's LAPIC
> explicitly if IO-APIC is disabled, to set up through-local-APIC.
> 
> Signed-off-by: Baoquan He <bhe@...hat.com>
> ---
>  arch/x86/kernel/apic/apic.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c
> index 880441f24146..7e613fb90630 100644
> --- a/arch/x86/kernel/apic/apic.c
> +++ b/arch/x86/kernel/apic/apic.c
> @@ -1521,7 +1521,7 @@ void setup_local_APIC(void)
>  	 * TODO: set up through-local-APIC from through-I/O-APIC? --macro
>  	 */
>  	value = apic_read(APIC_LVT0) & APIC_LVT_MASKED;
> -	if (!cpu && (pic_mode || !value)) {
> +	if (!cpu && (pic_mode || !value || skip_ioapic_setup)) {
>  		value = APIC_DM_EXTINT;
>  		apic_printk(APIC_VERBOSE, "enabled ExtINT on CPU#%d\n", cpu);
>  	} else {
> -- 
> 2.5.5
>