Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932079Ab0HaD3d (ORCPT ); Mon, 30 Aug 2010 23:29:33 -0400 Received: from mga11.intel.com ([192.55.52.93]:60225 "EHLO mga11.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756739Ab0HaD3c (ORCPT ); Mon, 30 Aug 2010 23:29:32 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.56,296,1280732400"; d="scan'208";a="602086184" Message-ID: <4C7C771A.2040603@intel.com> Date: Tue, 31 Aug 2010 11:29:30 +0800 From: Weidong Han User-Agent: Thunderbird 2.0.0.21 (Windows/20090302) MIME-Version: 1.0 To: "Siddha, Suresh B" CC: "H. Peter Anvin" , Ingo Molnar , Thomas Gleixner , LKML , "stable@kernel.org" Subject: Re: [patch 1/3] x86, intr-remap: set redirection hint in the IRTE References: <20100827181049.013051492@sbsiddha-MOBL3.sc.intel.com> <4C7B0DA6.2070204@intel.com> <1283188670.2695.13.camel@sbsiddha-MOBL3.sc.intel.com> In-Reply-To: <1283188670.2695.13.camel@sbsiddha-MOBL3.sc.intel.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3011 Lines: 77 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 >>> Cc: Weidong Han >>> Cc: # [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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/