Jan Beulich
2013-Jun-24 09:48 UTC
Re: [PATCH net-next V3 1/3] xen-netback: split event channels support for Xen backend driver
>>> On 22.05.13 at 18:34, Wei Liu <wei.liu2@citrix.com> wrote: > Netback and netfront only use one event channel to do TX / RX notification, > which may cause unnecessary wake-up of processing routines. This patch adds a > new feature called feature-split-event-channels to netback, enabling it to > handle TX and RX events separately. > > Netback will use tx_irq to notify guest for TX completion, rx_irq for RX > notification.While I can see the benefit for the frontend, does this really make a lot of a difference to the backend considering that both rx and tx handling get done on the same thread anyway? Jan> If frontend doesn''t support this feature, tx_irq equals to rx_irq. > > Signed-off-by: Wei Liu <wei.liu2@citrix.com> > --- > drivers/net/xen-netback/common.h | 13 ++++-- > drivers/net/xen-netback/interface.c | 85 ++++++++++++++++++++++++++++------- > drivers/net/xen-netback/netback.c | 14 ++++-- > drivers/net/xen-netback/xenbus.c | 41 ++++++++++++++--- > 4 files changed, 124 insertions(+), 29 deletions(-) > > diff --git a/drivers/net/xen-netback/common.h b/drivers/net/xen-netback/common.h > index 6102a6c..8a4d77e 100644 > --- a/drivers/net/xen-netback/common.h > +++ b/drivers/net/xen-netback/common.h > @@ -57,8 +57,12 @@ struct xenvif { > > u8 fe_dev_addr[6]; > > - /* Physical parameters of the comms window. */ > - unsigned int irq; > + /* When feature-split-event-channels = 0, tx_irq = rx_irq. */ > + unsigned int tx_irq; > + unsigned int rx_irq; > + /* Only used when feature-split-event-channels = 1 */ > + char tx_irq_name[IFNAMSIZ+4]; /* DEVNAME-tx */ > + char rx_irq_name[IFNAMSIZ+4]; /* DEVNAME-rx */ > > /* List of frontends to notify after a batch of frames sent. */ > struct list_head notify_list; > @@ -113,7 +117,8 @@ struct xenvif *xenvif_alloc(struct device *parent, > unsigned int handle); > > int xenvif_connect(struct xenvif *vif, unsigned long tx_ring_ref, > - unsigned long rx_ring_ref, unsigned int evtchn); > + unsigned long rx_ring_ref, unsigned int tx_evtchn, > + unsigned int rx_evtchn); > void xenvif_disconnect(struct xenvif *vif); > > void xenvif_get(struct xenvif *vif); > @@ -158,4 +163,6 @@ void xenvif_carrier_off(struct xenvif *vif); > /* Returns number of ring slots required to send an skb to the frontend */ > unsigned int xen_netbk_count_skb_slots(struct xenvif *vif, struct sk_buff > *skb); > > +extern bool separate_tx_rx_irq; > + > #endif /* __XEN_NETBACK__COMMON_H__ */ > diff --git a/drivers/net/xen-netback/interface.c > b/drivers/net/xen-netback/interface.c > index 82202c2..087d2db 100644 > --- a/drivers/net/xen-netback/interface.c > +++ b/drivers/net/xen-netback/interface.c > @@ -60,21 +60,39 @@ static int xenvif_rx_schedulable(struct xenvif *vif) > return xenvif_schedulable(vif) && !xen_netbk_rx_ring_full(vif); > } > > -static irqreturn_t xenvif_interrupt(int irq, void *dev_id) > +static irqreturn_t xenvif_tx_interrupt(int irq, void *dev_id) > { > struct xenvif *vif = dev_id; > > if (vif->netbk == NULL) > - return IRQ_NONE; > + return IRQ_HANDLED; > > xen_netbk_schedule_xenvif(vif); > > + return IRQ_HANDLED; > +} > + > +static irqreturn_t xenvif_rx_interrupt(int irq, void *dev_id) > +{ > + struct xenvif *vif = dev_id; > + > + if (vif->netbk == NULL) > + return IRQ_HANDLED; > + > if (xenvif_rx_schedulable(vif)) > netif_wake_queue(vif->dev); > > return IRQ_HANDLED; > } > > +static irqreturn_t xenvif_interrupt(int irq, void *dev_id) > +{ > + xenvif_tx_interrupt(irq, dev_id); > + xenvif_rx_interrupt(irq, dev_id); > + > + return IRQ_HANDLED; > +} > + > static int xenvif_start_xmit(struct sk_buff *skb, struct net_device *dev) > { > struct xenvif *vif = netdev_priv(dev); > @@ -125,13 +143,17 @@ static struct net_device_stats *xenvif_get_stats(struct > net_device *dev) > static void xenvif_up(struct xenvif *vif) > { > xen_netbk_add_xenvif(vif); > - enable_irq(vif->irq); > + enable_irq(vif->tx_irq); > + if (vif->tx_irq != vif->rx_irq) > + enable_irq(vif->rx_irq); > xen_netbk_check_rx_xenvif(vif); > } > > static void xenvif_down(struct xenvif *vif) > { > - disable_irq(vif->irq); > + disable_irq(vif->tx_irq); > + if (vif->tx_irq != vif->rx_irq) > + disable_irq(vif->rx_irq); > del_timer_sync(&vif->credit_timeout); > xen_netbk_deschedule_xenvif(vif); > xen_netbk_remove_xenvif(vif); > @@ -308,12 +330,13 @@ struct xenvif *xenvif_alloc(struct device *parent, > domid_t domid, > } > > int xenvif_connect(struct xenvif *vif, unsigned long tx_ring_ref, > - unsigned long rx_ring_ref, unsigned int evtchn) > + unsigned long rx_ring_ref, unsigned int tx_evtchn, > + unsigned int rx_evtchn) > { > int err = -ENOMEM; > > /* Already connected through? */ > - if (vif->irq) > + if (vif->tx_irq) > return 0; > > __module_get(THIS_MODULE); > @@ -322,13 +345,37 @@ int xenvif_connect(struct xenvif *vif, unsigned long > tx_ring_ref, > if (err < 0) > goto err; > > - err = bind_interdomain_evtchn_to_irqhandler( > - vif->domid, evtchn, xenvif_interrupt, 0, > - vif->dev->name, vif); > - if (err < 0) > - goto err_unmap; > - vif->irq = err; > - disable_irq(vif->irq); > + if (tx_evtchn == rx_evtchn) { > + /* feature-split-event-channels == 0 */ > + err = bind_interdomain_evtchn_to_irqhandler( > + vif->domid, tx_evtchn, xenvif_interrupt, 0, > + vif->dev->name, vif); > + if (err < 0) > + goto err_unmap; > + vif->tx_irq = vif->rx_irq = err; > + disable_irq(vif->tx_irq); > + } else { > + /* feature-split-event-channels == 1 */ > + snprintf(vif->tx_irq_name, sizeof(vif->tx_irq_name), > + "%s-tx", vif->dev->name); > + err = bind_interdomain_evtchn_to_irqhandler( > + vif->domid, tx_evtchn, xenvif_tx_interrupt, 0, > + vif->tx_irq_name, vif); > + if (err < 0) > + goto err_unmap; > + vif->tx_irq = err; > + disable_irq(vif->tx_irq); > + > + snprintf(vif->rx_irq_name, sizeof(vif->rx_irq_name), > + "%s-rx", vif->dev->name); > + err = bind_interdomain_evtchn_to_irqhandler( > + vif->domid, rx_evtchn, xenvif_rx_interrupt, 0, > + vif->rx_irq_name, vif); > + if (err < 0) > + goto err_tx_unbind; > + vif->rx_irq = err; > + disable_irq(vif->rx_irq); > + } > > xenvif_get(vif); > > @@ -342,6 +389,9 @@ int xenvif_connect(struct xenvif *vif, unsigned long > tx_ring_ref, > rtnl_unlock(); > > return 0; > +err_tx_unbind: > + unbind_from_irqhandler(vif->tx_irq, vif); > + vif->tx_irq = 0; > err_unmap: > xen_netbk_unmap_frontend_rings(vif); > err: > @@ -375,8 +425,13 @@ void xenvif_disconnect(struct xenvif *vif) > atomic_dec(&vif->refcnt); > wait_event(vif->waiting_to_free, atomic_read(&vif->refcnt) == 0); > > - if (vif->irq) { > - unbind_from_irqhandler(vif->irq, vif); > + if (vif->tx_irq) { > + if (vif->tx_irq == vif->rx_irq) > + unbind_from_irqhandler(vif->tx_irq, vif); > + else { > + unbind_from_irqhandler(vif->tx_irq, vif); > + unbind_from_irqhandler(vif->rx_irq, vif); > + } > /* vif->irq is valid, we had a module_get in > * xenvif_connect. > */ > diff --git a/drivers/net/xen-netback/netback.c > b/drivers/net/xen-netback/netback.c > index 2d9477f..82576ff 100644 > --- a/drivers/net/xen-netback/netback.c > +++ b/drivers/net/xen-netback/netback.c > @@ -47,6 +47,13 @@ > #include <asm/xen/hypercall.h> > #include <asm/xen/page.h> > > +/* Provide an option to disable split event channels at load time as > + * event channels are limited resource. Split event channels are > + * enabled by default. > + */ > +bool separate_tx_rx_irq = 1; > +module_param(separate_tx_rx_irq, bool, 0644); > + > /* > * This is the maximum slots a skb can have. If a guest sends a skb > * which exceeds this limit it is considered malicious. > @@ -662,7 +669,7 @@ static void xen_netbk_rx_action(struct xen_netbk *netbk) > { > struct xenvif *vif = NULL, *tmp; > s8 status; > - u16 irq, flags; > + u16 flags; > struct xen_netif_rx_response *resp; > struct sk_buff_head rxq; > struct sk_buff *skb; > @@ -771,7 +778,6 @@ static void xen_netbk_rx_action(struct xen_netbk *netbk) > sco->meta_slots_used); > > RING_PUSH_RESPONSES_AND_CHECK_NOTIFY(&vif->rx, ret); > - irq = vif->irq; > if (ret && list_empty(&vif->notify_list)) > list_add_tail(&vif->notify_list, ¬ify); > > @@ -783,7 +789,7 @@ static void xen_netbk_rx_action(struct xen_netbk *netbk) > } > > list_for_each_entry_safe(vif, tmp, ¬ify, notify_list) { > - notify_remote_via_irq(vif->irq); > + notify_remote_via_irq(vif->rx_irq); > list_del_init(&vif->notify_list); > } > > @@ -1762,7 +1768,7 @@ static void make_tx_response(struct xenvif *vif, > vif->tx.rsp_prod_pvt = ++i; > RING_PUSH_RESPONSES_AND_CHECK_NOTIFY(&vif->tx, notify); > if (notify) > - notify_remote_via_irq(vif->irq); > + notify_remote_via_irq(vif->tx_irq); > } > > static struct xen_netif_rx_response *make_rx_response(struct xenvif *vif, > diff --git a/drivers/net/xen-netback/xenbus.c b/drivers/net/xen-netback/xenbus.c > index d230c14..04bd860 100644 > --- a/drivers/net/xen-netback/xenbus.c > +++ b/drivers/net/xen-netback/xenbus.c > @@ -122,6 +122,16 @@ static int netback_probe(struct xenbus_device *dev, > goto fail; > } > > + /* > + * Split event channels support, this is optional so it is not > + * put inside the above loop. > + */ > + err = xenbus_printf(XBT_NIL, dev->nodename, > + "feature-split-event-channels", > + "%u", separate_tx_rx_irq); > + if (err) > + pr_debug("Error writing feature-split-event-channels"); > + > err = xenbus_switch_state(dev, XenbusStateInitWait); > if (err) > goto fail; > @@ -393,21 +403,36 @@ static int connect_rings(struct backend_info *be) > struct xenvif *vif = be->vif; > struct xenbus_device *dev = be->dev; > unsigned long tx_ring_ref, rx_ring_ref; > - unsigned int evtchn, rx_copy; > + unsigned int tx_evtchn, rx_evtchn, rx_copy; > int err; > int val; > > err = xenbus_gather(XBT_NIL, dev->otherend, > "tx-ring-ref", "%lu", &tx_ring_ref, > - "rx-ring-ref", "%lu", &rx_ring_ref, > - "event-channel", "%u", &evtchn, NULL); > + "rx-ring-ref", "%lu", &rx_ring_ref, NULL); > if (err) { > xenbus_dev_fatal(dev, err, > - "reading %s/ring-ref and event-channel", > + "reading %s/ring-ref", > dev->otherend); > return err; > } > > + /* Try split event channels first, then single event channel. */ > + err = xenbus_gather(XBT_NIL, dev->otherend, > + "event-channel-tx", "%u", &tx_evtchn, > + "event-channel-rx", "%u", &rx_evtchn, NULL); > + if (err < 0) { > + err = xenbus_scanf(XBT_NIL, dev->otherend, > + "event-channel", "%u", &tx_evtchn); > + if (err < 0) { > + xenbus_dev_fatal(dev, err, > + "reading %s/event-channel(-tx/rx)", > + dev->otherend); > + return err; > + } > + rx_evtchn = tx_evtchn; > + } > + > err = xenbus_scanf(XBT_NIL, dev->otherend, "request-rx-copy", "%u", > &rx_copy); > if (err == -ENOENT) { > @@ -454,11 +479,13 @@ static int connect_rings(struct backend_info *be) > vif->csum = !val; > > /* Map the shared frame, irq etc. */ > - err = xenvif_connect(vif, tx_ring_ref, rx_ring_ref, evtchn); > + err = xenvif_connect(vif, tx_ring_ref, rx_ring_ref, > + tx_evtchn, rx_evtchn); > if (err) { > xenbus_dev_fatal(dev, err, > - "mapping shared-frames %lu/%lu port %u", > - tx_ring_ref, rx_ring_ref, evtchn); > + "mapping shared-frames %lu/%lu port tx %u rx %u", > + tx_ring_ref, rx_ring_ref, > + tx_evtchn, rx_evtchn); > return err; > } > return 0; > -- > 1.7.10.4