Messages in this thread | | | Date | Fri, 12 Sep 2014 11:58:47 +0100 | From | David Vrabel <> | Subject | Re: [PATCH RFC v2 5/5] xen, blkback: negotiate of the number of block rings with the frontend |
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On 12/09/14 00:57, 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. [...] > --- 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);
This BUG_ON() isn't useful.
> + 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); > + if (err) > + xenbus_dev_error(blkif->be->dev, err, "writing %s/nr_supported_hw_queues", > + blkif->be->dev->nodename); > + > + xenbus_transaction_end(xbt, 0);
Transactions are expensive and not needed to write a single key.
Can you use the same key names as netback (multi-queue-max-queues I think)? I don't see why we can't use a common set of key names for this.
See interface/io/netif.h for full set of keys VIFs use.
David
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