linux-kernel - Re: [patch 1/3] x86, intr-remap: set redirection hint in the IRTE

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Date:	Mon, 30 Aug 2010 09:35:44 +0800
From:	Weidong Han <weidong.han@...el.com>
To:	"Siddha, Suresh B" <suresh.b.siddha@...el.com>
CC:	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	LKML <linux-kernel@...r.kernel.org>,
	"stable@...nel.org" <stable@...nel.org>
Subject: Re: [patch 1/3] x86, intr-remap: set redirection hint in the IRTE

Siddha, Suresh B wrote:
> Currently the redirection hint in the interrupt-remapping table entry
> is set to 0, which means the remapped interrupt is directed to the
> processors listed in the destination. So in logical flat mode
> in the presence of intr-remapping, this results in a single
> interrupt multi-casted to multiple cpu's as specified by the destination
> bit mask. But what we really want is to send that interrupt to one of the cpus
> based on the lowest priority delivery mode.
>
> Set the redirection hint in the IRTE to '1' to indicate that we want
> the remapped interrupt to be directed to only one of the processors
> listed in the destination.
>
> This fixes the issue of same interrupt getting delivered to multiple cpu's
> in the logical flat mode in the presence of interrupt-remapping. While
> there is no functional issue observed with this behavior, this will
> impact performance of such configurations (<=8 cpu's using logical flat
> mode in the presence of interrupt-remapping)
>
> Signed-off-by: Suresh Siddha <suresh.b.siddha@...el.com>
> Cc: Weidong Han <weidong.han@...el.com>
> Cc: <stable@...nel.org> # [v2.6.32+]
> ---
>
> diff --git a/arch/x86/kernel/apic/io_apic.c b/arch/x86/kernel/apic/io_apic.c
> index f1efeba..90f8a75 100644
> --- a/arch/x86/kernel/apic/io_apic.c
> +++ b/arch/x86/kernel/apic/io_apic.c
> @@ -1392,6 +1392,7 @@ int setup_ioapic_entry(int apic_id, int irq,
>  		irte.dlvry_mode = apic->irq_delivery_mode;
>  		irte.vector = vector;
>  		irte.dest_id = IRTE_DEST(destination);
> +		irte.redir_hint = 1;
>  
>  		/* Set source-id of interrupt request */
>  		set_ioapic_sid(&irte, apic_id);
> @@ -3343,6 +3344,7 @@ static int msi_compose_msg(struct pci_dev *pdev, unsigned int irq,
>  		irte.dlvry_mode = apic->irq_delivery_mode;
>  		irte.vector = cfg->vector;
>  		irte.dest_id = IRTE_DEST(dest);
> +		irte.redir_hint = 1;
>  
>  		/* Set source-id of interrupt request */
>  		if (pdev)
>
>
>   
Hi Suresh,

Your patch always sets redir_hint to 1 for all delivery modes. Why not 
check if it's lowest priority delivery mode before set redit_hint to 1?

Regards,
Weidong


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