Messages in this thread | | | Date | Tue, 31 Aug 2010 11:29:30 +0800 | From | Weidong Han <> | Subject | Re: [patch 1/3] x86, intr-remap: set redirection hint in the IRTE |
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Siddha, Suresh B wrote: > On Sun, 2010-08-29 at 18:47 -0700, Han, Weidong wrote: > >> 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@intel.com> >>> Cc: Weidong Han <weidong.han@intel.com> >>> Cc: <stable@kernel.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, >> >> I think it needs to set redir_hint only for lowest priority delivery >> mode. Why set it for all delivery modes? >> > > Weidong, For all the IRQ types (irrespective of lowest priority/fixed > mode etc) x86 linux kernel doesn't use irq multi-cast model (which is > what irte.redir_hint == 0 means). So as it is not particularly tied with > lowest priority mode (irte.redir_hint is equally applicable for fixed > mode though we don't use it currently), it makes sense to set it > unconditionally for the current usages. > > > Thanks for your explanation. It's ok.
Regards, Weidong
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