From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Michael S. Tsirkin" Subject: Re: [PATCH 08/16] virtio_ring: virtqueue_add_outbuf / virtqueue_add_inbuf. Date: Thu, 21 Feb 2013 19:09:03 +0200 Message-ID: <20130221170902.GA27097@redhat.com> References: <1361260594-601-1-git-send-email-rusty@rustcorp.com.au> <1361260594-601-9-git-send-email-rusty@rustcorp.com.au> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline In-Reply-To: <1361260594-601-9-git-send-email-rusty@rustcorp.com.au> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: virtualization-bounces@lists.linux-foundation.org Errors-To: virtualization-bounces@lists.linux-foundation.org To: Rusty Russell Cc: Paolo Bonzini , linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org List-Id: virtualization@lists.linuxfoundation.org On Tue, Feb 19, 2013 at 06:26:26PM +1030, Rusty Russell wrote: > These are specialized versions of virtqueue_add_buf(), which cover > over 50% of cases and are far clearer. > > In particular, the scatterlists passed to these functions don't have > to be clean (ie. we ignore end markers). > > FIXME: I'm not sure about the unclean sglist bit. I had a more > ambitious one which conditionally ignored end markers in the iterator, > but it was ugly and I suspect this is just as fast. Maybe we should > just fix all the drivers? > > Signed-off-by: Rusty Russell Looking at code, it seems that most users really have a single sg, in low memory. So how about simply passing void * instead of sg? Whoever has multiple sgs can use the rich interface. Long term we might optimize this unrolling some loops, I think I saw this giving a small performance gain for -net. > --- > drivers/virtio/virtio_ring.c | 58 ++++++++++++++++++++++++++++++++++++++++++ > include/linux/virtio.h | 10 ++++++++ > 2 files changed, 68 insertions(+) > > diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c > index c537385..fb282b5 100644 > --- a/drivers/virtio/virtio_ring.c > +++ b/drivers/virtio/virtio_ring.c > @@ -345,6 +345,64 @@ int virtqueue_add_sgs(struct virtqueue *_vq, > EXPORT_SYMBOL_GPL(virtqueue_add_sgs); > > /** > + * virtqueue_add_outbuf - expose output buffers to other end > + * @vq: the struct virtqueue we're talking about. > + * @sgs: array of scatterlists (need not be terminated!) > + * @num: the number of scatterlists readable by other side > + * @data: the token identifying the buffer. > + * @gfp: how to do memory allocations (if necessary). > + * > + * Caller must ensure we don't call this with other virtqueue operations > + * at the same time (except where noted). > + * > + * Returns zero or a negative error (ie. ENOSPC, ENOMEM). > + */ > +int virtqueue_add_outbuf(struct virtqueue *vq, > + struct scatterlist sg[], unsigned int num, > + void *data, > + gfp_t gfp) > +{ > + unsigned int i; > + > + /* We're about to iterate, so this is pretty cheap. */ > + for (i = 0; i < num - 1; i++) > + sg_unmark_end(sg + i); > + sg_mark_end(sg + i); > + > + return virtqueue_add(vq, &sg, num, 1, 0, data, gfp); > +} > +EXPORT_SYMBOL_GPL(virtqueue_add_outbuf); > + > +/** > + * virtqueue_add_inbuf - expose input buffers to other end > + * @vq: the struct virtqueue we're talking about. > + * @sgs: array of scatterlists (need not be terminated!) > + * @num: the number of scatterlists writable by other side > + * @data: the token identifying the buffer. > + * @gfp: how to do memory allocations (if necessary). > + * > + * Caller must ensure we don't call this with other virtqueue operations > + * at the same time (except where noted). > + * > + * Returns zero or a negative error (ie. ENOSPC, ENOMEM). > + */ > +int virtqueue_add_inbuf(struct virtqueue *vq, > + struct scatterlist sg[], unsigned int num, > + void *data, > + gfp_t gfp) > +{ > + unsigned int i; > + > + /* We're about to iterate, so this is pretty cheap. */ > + for (i = 0; i < num - 1; i++) > + sg_unmark_end(sg + i); > + sg_mark_end(sg + i); > + > + return virtqueue_add(vq, &sg, num, 0, 1, data, gfp); > +} > +EXPORT_SYMBOL_GPL(virtqueue_add_inbuf); > + > +/** > * virtqueue_kick_prepare - first half of split virtqueue_kick call. > * @vq: the struct virtqueue > * > diff --git a/include/linux/virtio.h b/include/linux/virtio.h > index 6eff15b..b442500 100644 > --- a/include/linux/virtio.h > +++ b/include/linux/virtio.h > @@ -40,6 +40,16 @@ int virtqueue_add_buf(struct virtqueue *vq, > void *data, > gfp_t gfp); > > +int virtqueue_add_outbuf(struct virtqueue *vq, > + struct scatterlist sg[], unsigned int num, > + void *data, > + gfp_t gfp); > + > +int virtqueue_add_inbuf(struct virtqueue *vq, > + struct scatterlist sg[], unsigned int num, > + void *data, > + gfp_t gfp); > + > int virtqueue_add_sgs(struct virtqueue *vq, > struct scatterlist *sgs[], > unsigned int out_sgs, > -- > 1.7.10.4