Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756097Ab0H3RS3 (ORCPT ); Mon, 30 Aug 2010 13:18:29 -0400 Received: from mga03.intel.com ([143.182.124.21]:28095 "EHLO mga03.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756050Ab0H3RS2 (ORCPT ); Mon, 30 Aug 2010 13:18:28 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.56,293,1280732400"; d="scan'208";a="318804301" Subject: Re: [patch 1/3] x86, intr-remap: set redirection hint in the IRTE From: Suresh Siddha Reply-To: Suresh Siddha To: "Han, Weidong" Cc: "H. Peter Anvin" , Ingo Molnar , Thomas Gleixner , LKML , "stable@kernel.org" In-Reply-To: <4C7B0DA6.2070204@intel.com> References: <20100827181049.013051492@sbsiddha-MOBL3.sc.intel.com> <4C7B0DA6.2070204@intel.com> Content-Type: text/plain Organization: Intel Corp Date: Mon, 30 Aug 2010 10:17:50 -0700 Message-Id: <1283188670.2695.13.camel@sbsiddha-MOBL3.sc.intel.com> Mime-Version: 1.0 X-Mailer: Evolution 2.26.3 (2.26.3-1.fc11) Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2887 Lines: 68 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, suresh -- 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/