From mboxrd@z Thu Jan 1 00:00:00 1970 From: Will Deacon Subject: Re: [PATCH 3/5] iommu: Limit iommu_attach/detach_device to devices with their own group Date: Mon, 2 Feb 2015 16:45:46 +0000 Message-ID: <20150202164545.GH31847@arm.com> References: <1422317339-22620-1-git-send-email-joro@8bytes.org> <1422317339-22620-4-git-send-email-joro@8bytes.org> <20150128143523.GR1569@arm.com> <20150130122814.GC3702@8bytes.org> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline In-Reply-To: <20150130122814.GC3702-zLv9SwRftAIdnm+yROfE0A@public.gmane.org> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: iommu-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org Errors-To: iommu-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org To: Joerg Roedel Cc: "jroedel-l3A5Bk7waGM@public.gmane.org" , Laurent Pinchart , Heiko Stuebner , Arnd Bergmann , "linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , "iommu-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org" , Thierry Reding , Kukjin Kim , David Woodhouse List-Id: iommu@lists.linux-foundation.org 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