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Date: Mon, 2 Feb 2015 16:45:46 +0000
From: Will Deacon <will.deacon@arm.com>
To: Joerg Roedel <joro@8bytes.org>
Cc: "iommu@lists.linux-foundation.org" <iommu@lists.linux-foundation.org>,
        Kukjin Kim <kgene@kernel.org>, David Woodhouse <dwmw2@infradead.org>,
        Heiko Stuebner <heiko@sntech.de>, Hiroshi Doyu <hdoyu@nvidia.com>,
        Thierry Reding <thierry.reding@gmail.com>,
        Alex Williamson <alex.williamson@redhat.com>,
        Arnd Bergmann <arnd@arndb.de>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Robin Murphy <Robin.Murphy@arm.com>,
        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: <20150202164545.GH31847@arm.com>
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On Fri, Jan 30, 2015 at 12:28:14PM +0000, Joerg Roedel wrote:
> 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?

No problem, it just seemed a bit redundant to have two ways of describing
the same thing and having the pain of keeping them in sync with each other.

Will