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Date: Fri, 30 Jan 2015 13:28:14 +0100
From: Joerg Roedel <joro@8bytes.org>
To: Will Deacon <will.deacon@arm.com>
Cc: "iommu@lists.linux-foundation.org" <iommu@lists.linux-foundation.org>,
        Kukjin Kim <kgene@kernel.org>, David Woodhouse <dwmw2@infradead.org>,
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        Laurent Pinchart <laurent.pinchart@ideasonboard.com>,
        "jroedel@suse.de" <jroedel@suse.de>
Subject: Re: [PATCH 3/5] iommu: Limit iommu_attach/detach_device to devices
 with their own group
Message-ID: <20150130122814.GC3702@8bytes.org>
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 <20150128143523.GR1569@arm.com>
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On Wed, Jan 28, 2015 at 02:35:24PM +0000, Will Deacon wrote:
> On Tue, Jan 27, 2015 at 12:08:57AM +0000, Joerg Roedel wrote:
> > @@ -51,6 +51,7 @@ struct iommu_group {
> >  	void (*iommu_data_release)(void *iommu_data);
> >  	char *name;
> >  	int id;
> > +	unsigned dev_cnt;
> 
> Is this actually used on a fast path, or can we just inspect the list of
> devices on the group instead?

Not really a fast path, but we have to hold the group mutex while
traversing the list, which could hurt performance somewhere else. Are
these 4 bytes a problem?


	Joerg