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Message-Id: <51C8320902000078000DFF4E@nat28.tlf.novell.com>
Date: Mon, 24 Jun 2013 10:48:25 +0100
From: "Jan Beulich" <JBeulich@...e.com>
To: "Wei Liu" <wei.liu2@...rix.com>
Cc: <david.vrabel@...rix.com>, <ian.campbell@...rix.com>,
<xen-devel@...ts.xen.org>, <annie.li@...cle.com>,
<konrad.wilk@...cle.com>, <netdev@...r.kernel.org>
Subject: 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@...rix.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@...rix.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
--
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