lkml.org 
[lkml]   [2014]   [Oct]   [1]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH RFC v2 5/5] xen, blkback: negotiate of the number of block rings with the frontend
On Fri, Sep 12, 2014 at 01:57:24AM +0200, Arianna Avanzini wrote:
> This commit lets the backend driver advertise the number of available
> hardware queues; it also implements gathering from the frontend driver
> the number of rings actually available for mapping.
>
> Signed-off-by: Arianna Avanzini <avanzini.arianna@gmail.com>
> ---
> drivers/block/xen-blkback/xenbus.c | 44 +++++++++++++++++++++++++++++++++++++-
> 1 file changed, 43 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/block/xen-blkback/xenbus.c b/drivers/block/xen-blkback/xenbus.c
> index a4f13cc..9ff6ced 100644
> --- a/drivers/block/xen-blkback/xenbus.c
> +++ b/drivers/block/xen-blkback/xenbus.c
> @@ -477,6 +477,34 @@ static void xen_vbd_free(struct xen_vbd *vbd)
> vbd->bdev = NULL;
> }
>
> +static int xen_advertise_hw_queues(struct xen_blkif *blkif,
> + struct request_queue *q)
> +{
> + struct xen_vbd *vbd = &blkif->vbd;
> + struct xenbus_transaction xbt;
> + int err;
> +
> + if (q && q->mq_ops)
> + vbd->nr_supported_hw_queues = q->nr_hw_queues;
> +
> + err = xenbus_transaction_start(&xbt);
> + if (err) {
> + BUG_ON(!blkif->be);
> + xenbus_dev_fatal(blkif->be->dev, err, "starting transaction (hw queues)");
> + return err;
> + }
> +
> + err = xenbus_printf(xbt, blkif->be->dev->nodename, "nr_supported_hw_queues", "%u",
> + blkif->vbd.nr_supported_hw_queues);

I would (as David had mentioned) use the same keys that netfront is using for negotiating
this.

Plus that means you can copy-n-paste the text from netif.h to blkif.h instead of having
to write it :-)

> + if (err)
> + xenbus_dev_error(blkif->be->dev, err, "writing %s/nr_supported_hw_queues",
> + blkif->be->dev->nodename);
> +
> + xenbus_transaction_end(xbt, 0);
> +
> + return err;
> +}
> +
> static int xen_vbd_create(struct xen_blkif *blkif, blkif_vdev_t handle,
> unsigned major, unsigned minor, int readonly,
> int cdrom)
> @@ -484,6 +512,7 @@ static int xen_vbd_create(struct xen_blkif *blkif, blkif_vdev_t handle,
> struct xen_vbd *vbd;
> struct block_device *bdev;
> struct request_queue *q;
> + int err;
>
> vbd = &blkif->vbd;
> vbd->handle = handle;
> @@ -522,6 +551,10 @@ static int xen_vbd_create(struct xen_blkif *blkif, blkif_vdev_t handle,
> if (q && blk_queue_secdiscard(q))
> vbd->discard_secure = true;
>
> + err = xen_advertise_hw_queues(blkif, q);
> + if (err)
> + return -ENOENT;
> +
> DPRINTK("Successful creation of handle=%04x (dom=%u)\n",
> handle, blkif->domid);
> return 0;
> @@ -935,7 +968,16 @@ static int connect_ring(struct backend_info *be)
>
> DPRINTK("%s", dev->otherend);
>
> - blkif->nr_rings = 1;
> + err = xenbus_gather(XBT_NIL, dev->otherend, "nr_blk_rings",
> + "%u", &blkif->nr_rings, NULL);
> + if (err) {
> + /*
> + * Frontend does not support multiqueue; force compatibility
> + * mode of the driver.
> + */
> + blkif->vbd.nr_supported_hw_queues = 0;
> + blkif->nr_rings = 1;
I would add also:

pr_debug("Advertised %u queues, fronted deaf - using one ring.\n");

To make it easier during debugging/testing to figure out why the frontend
does not seem to use it (and having an easy way to figure out why).

> + }
>
> ring_ref = kzalloc(sizeof(unsigned long) * blkif->nr_rings, GFP_KERNEL);
> if (!ring_ref)
> --
> 2.1.0
>


\
 
 \ /
  Last update: 2014-10-01 23:01    [W:0.114 / U:1.892 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site