linux-kernel - Re: [PATCH 2/4] Intel iommu: Speed up processing of the identity

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Message-ID: <4D93CBEE.5020201@sgi.com>
Date:	Wed, 30 Mar 2011 17:33:50 -0700
From:	Mike Travis <travis@....com>
To:	Chris Wright <chrisw@...s-sol.org>
Cc:	David Woodhouse <dwmw2@...radead.org>,
	Jesse Barnes <jbarnes@...tuousgeek.org>,
	linux-pci@...r.kernel.org, iommu@...ts.linux-foundation.org,
	Mike Habeck <habeck@....com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/4] Intel iommu: Speed up processing of the identity_mapping
 function v2

Subject: Intel iommu: Speed up processing of the identity_mapping function

    When there are a large count of PCI devices, and the pass
    through option for iommu is set, much time is spent in the
    identity_mapping function hunting though the iommu domains to
    check if a specific device is "identity mapped".

    Speed up the function by checking the cached info to see if
    it's mapped to the static identity domain.

Signed-off-by: Mike Travis <travis@....com>
---
 drivers/pci/intel-iommu.c |    6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

--- linux-2.6.32.orig/drivers/pci/intel-iommu.c
+++ linux-2.6.32/drivers/pci/intel-iommu.c
@@ -2124,10 +2124,10 @@ static int identity_mapping(struct pci_d
 	if (likely(!iommu_identity_mapping))
 		return 0;
 
+	info = pdev->dev.archdata.iommu;
+	if (info && info != DUMMY_DEVICE_DOMAIN_INFO)
+		return (info->domain == si_domain);
 
-	list_for_each_entry(info, &si_domain->devices, link)
-		if (info->dev == pdev)
-			return 1;
 	return 0;
 }
 

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