From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Date: Wed, 10 Apr 2019 17:12:54 +0200 From: Halil Pasic Subject: Re: [RFC PATCH 10/12] virtio/s390: consolidate DMA allocations In-Reply-To: <20190410104649.12cdbcba.cohuck@redhat.com> References: <20190404231622.52531-1-pasic@linux.ibm.com> <20190404231622.52531-11-pasic@linux.ibm.com> <20190410104649.12cdbcba.cohuck@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Message-Id: <20190410171254.71206015@oc2783563651> Sender: kvm-owner@vger.kernel.org List-Archive: List-Post: To: Cornelia Huck Cc: kvm@vger.kernel.org, linux-s390@vger.kernel.org, Martin Schwidefsky , Sebastian Ott , virtualization@lists.linux-foundation.org, Christian Borntraeger , Viktor Mihajlovski , Vasily Gorbik , Janosch Frank , Claudio Imbrenda , Farhan Ali , Eric Farman List-ID: On Wed, 10 Apr 2019 10:46:49 +0200 Cornelia Huck wrote: > On Fri, 5 Apr 2019 01:16:20 +0200 > Halil Pasic wrote: > > > We can reduce the number of DMA allocations by pulling the bits > > of memory that belongs to virtio_ccw_device and needs to be DMA > > memory into a single area. > > That makes a lot of sense (maybe start with introducing the dma area > from the beginning?), but... > Yeah, as I wrote at #7 once we are in clear how the code should look like in the end, it might make sense to squash a couple of patches together. > > > > Signed-off-by: Halil Pasic > > --- > > drivers/s390/virtio/virtio_ccw.c | 48 ++++++++++++++-------------------------- > > 1 file changed, 16 insertions(+), 32 deletions(-) > > > > diff --git a/drivers/s390/virtio/virtio_ccw.c b/drivers/s390/virtio/virtio_ccw.c > > index aa45a6a027ae..7268149f2ee8 100644 > > --- a/drivers/s390/virtio/virtio_ccw.c > > +++ b/drivers/s390/virtio/virtio_ccw.c > > @@ -49,12 +49,12 @@ struct vq_config_block { > > struct vcdev_dma_area { > > unsigned long indicators; > > unsigned long indicators2; > > + struct vq_config_block config_block; > > + __u8 status; /* TODO check __aligned(8); */ > > ...I think that needs attention. Yes I wanted to discuss this with you. I could not find anything in the virtio spec that would put requirements on how this status field needs to be aligned. But I did not look to hard. The ccw.cda can hold an arbitrary data address AFAIR (for indirect, of course we do have alignment requirements). Apparently status used to be a normal field, and became a pointer with 73fa21ea4fc6 "KVM: s390: Dynamic allocation of virtio-ccw I/O data." (Cornelia Huck, 2013-01-07). I could not quite figure out why. So maybe dropping the TODO comment will do just fine. What do you think? Regards, Halil > > > }; > > > > struct virtio_ccw_device { > > struct virtio_device vdev; > > - __u8 *status; > > - dma_addr_t status_dma_addr; > > __u8 config[VIRTIO_CCW_CONFIG_SIZE]; > > struct ccw_device *cdev; > > __u32 curr_io; >