From mboxrd@z Thu Jan 1 00:00:00 1970 From: "gregkh-hQyY1W1yCW8ekmWlsbkhG0B+6BGkLq7r@public.gmane.org" Subject: Re: [PATCH 2/9] Move dma_ops from archdata into struct device Date: Wed, 11 Jan 2017 21:29:49 +0100 Message-ID: <20170111202949.GA17895@kroah.com> References: <20170111005648.14988-1-bart.vanassche@sandisk.com> <20170111005648.14988-3-bart.vanassche@sandisk.com> <20170111064624.GA26893@kroah.com> <1484157772.2619.12.camel@sandisk.com> Mime-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Return-path: Content-Disposition: inline In-Reply-To: <1484157772.2619.12.camel-XdAiOPVOjttBDgjK7y7TUQ@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: Bart Van Assche Cc: "linux-mips-6z/3iImG2C8G8FEW9MqTrA@public.gmane.org" , "dalias-8zAoT0mYgF4@public.gmane.org" , "linux-ia64-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , "a-jacquiot-l0cyMroinI0@public.gmane.org" , "catalin.marinas-5wv7dgnIgG8@public.gmane.org" , "will.deacon-5wv7dgnIgG8@public.gmane.org" , "x86-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org" , "mulix-BzGcCpaT2IbYtjvyW6yDsg@public.gmane.org" , "dhowells-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org" , "jcmvbkbc-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org" , "hpa-YMNOUZJC4hwAvxtiuMwx3w@public.gmane.org" , "sparclinux-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , "tglx-hfZtesqFncYOwBW4kG4KsQ@public.gmane.org" , "egtvedt-BrfabpQBY5qlHtIdYg32fQ@public.gmane.org" , "jonas-A9uVI2HLR7kOP4wsBPIw7w@public.gmane.org" , "linux-s390-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , "jesper.nilsson-VrBV9hrLPhE@public.gmane.org" , "linux-am33-list-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org" "linux-c6x-dev-jPsnJVOj+W6hPH1hqNUYSQ@public.gmane.org" List-Id: linux-rdma@vger.kernel.org On Wed, Jan 11, 2017 at 06:03:15PM +0000, Bart Van Assche wrote: > On Wed, 2017-01-11 at 07:46 +0100, Greg Kroah-Hartman wrote: > > On Tue, Jan 10, 2017 at 04:56:41PM -0800, Bart Van Assche wrote: > > > Several RDMA drivers, e.g. drivers/infiniband/hw/qib, use the CPU to > > > transfer data between memory and PCIe adapter. Because of performance > > > reasons it is important that the CPU cache is not flushed when such > > > drivers transfer data. Make this possible by allowing these drivers to > > > override the dma_map_ops pointer. Additionally, introduce the function > > > set_dma_ops() that will be used by a later patch in this series. > > > = > > > Signed-off-by: Bart Van Assche > > > Cc: [ ... ] > > = > > That's a crazy cc: list, you should break this up into smaller pieces, > > otherwise it's going to bounce... > = > That's a subset of what scripts/get_maintainer.pl came up with. Suggestio= ns > for a more appropriate cc-list for a patch like this that touches all > architectures would be welcome. You need to break this patch up into a series that can be applied in sequence, don't change everything all at once. That's a mess to merge, as you are finding out. > > > diff --git a/include/linux/device.h b/include/linux/device.h > > > index 491b4c0ca633..c7cb225d36b0 100644 > > > --- a/include/linux/device.h > > > +++ b/include/linux/device.h > > > @@ -885,6 +885,8 @@ struct dev_links_info { > > > =A0 * a higher-level representation of the device. > > > =A0 */ > > > =A0struct device { > > > + const struct dma_map_ops *dma_ops; /* See also get_dma_ops() */ > > > + > > > =A0 struct device *parent; > > > =A0 > > > =A0 struct device_private *p; > > = > > Why not put this new pointer down with the other dma fields in this > > structure?=A0=A0Any specific reason it needs to be first? > = > Are there CPU architectures for which access to the first member of a > structure can be encoded and/or executed more efficiently than access to > other members of a structure? If not, I'm fine with moving the new pointer > further down. Why do you think that your pointer is the one that gets to be "most efficient"? :) Seriously, no, it doesn't matter at all, it's all just pointer math which is very fast. Put it with the other stuff please, don't try to optimize something without ever measuring it. thanks, greg k-h