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Merge branch 'xen-netback'

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Wei Liu says:

====================
xen-netback: switch to NAPI + kthread 1:1 model

This series implements NAPI + kthread 1:1 model for Xen netback.

This model
 - provides better scheduling fairness among vifs
 - is prerequisite for implementing multiqueue for Xen network driver

The second patch has the real meat:
 - make use of NAPI to mitigate interrupt
 - kthreads are not bound to CPUs any more, so that we can take
   advantage of backend scheduler and trust it to do the right thing

Benchmark is done on a Dell T3400 workstation with 4 cores, running 4
DomUs. Netserver runs in Dom0. DomUs do netperf to Dom0 with
following command: /root/netperf -H Dom0 -fm -l120

IRQs are distributed to 4 cores by hand in the new model, while in the
old model vifs are automatically distributed to 4 kthreads.

* New model
%Cpu0  :  0.5 us, 20.3 sy,  0.0 ni, 28.9 id,  0.0 wa,  0.0 hi, 24.4 si, 25.9 st
%Cpu1  :  0.5 us, 17.8 sy,  0.0 ni, 28.8 id,  0.0 wa,  0.0 hi, 27.7 si, 25.1 st
%Cpu2  :  0.5 us, 18.8 sy,  0.0 ni, 30.7 id,  0.0 wa,  0.0 hi, 22.9 si, 27.1 st
%Cpu3  :  0.0 us, 20.1 sy,  0.0 ni, 30.4 id,  0.0 wa,  0.0 hi, 22.7 si, 26.8 st
Throughputs: 2027.89 2025.95 2018.57 2016.23 aggregated: 8088.64

* Old model
%Cpu0  :  0.5 us, 68.8 sy,  0.0 ni, 16.1 id,  0.5 wa,  0.0 hi,  2.8 si, 11.5 st
%Cpu1  :  0.4 us, 45.1 sy,  0.0 ni, 31.1 id,  0.4 wa,  0.0 hi,  2.1 si, 20.9 st
%Cpu2  :  0.9 us, 44.8 sy,  0.0 ni, 30.9 id,  0.0 wa,  0.0 hi,  1.3 si, 22.2 st
%Cpu3  :  0.8 us, 46.4 sy,  0.0 ni, 28.3 id,  1.3 wa,  0.0 hi,  2.1 si, 21.1 st
Throughputs: 1899.14 2280.43 1963.33 1893.47 aggregated: 8036.37

We can see that the impact is mainly on CPU usage. The new model moves
processing from kthread to NAPI (software interrupt).
====================

Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
David S. Miller 2013-08-29 01:18:52 -04:00
commit 823a19e0cf
3 changed files with 449 additions and 677 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

154
drivers/net/xen-netback/common.h
View File

@ -45,31 +45,109 @@
#include <xen/grant_table.h>
#include <xen/xenbus.h>
struct xen_netbk;
typedef unsigned int pending_ring_idx_t;
#define INVALID_PENDING_RING_IDX (~0U)
/* For the head field in pending_tx_info: it is used to indicate
* whether this tx info is the head of one or more coalesced requests.
*
* When head != INVALID_PENDING_RING_IDX, it means the start of a new
* tx requests queue and the end of previous queue.
*
* An example sequence of head fields (I = INVALID_PENDING_RING_IDX):
*
* ...|0 I I I|5 I|9 I I I|...
* -->|<-INUSE----------------
*
* After consuming the first slot(s) we have:
*
* ...|V V V V|5 I|9 I I I|...
* -----FREE->|<-INUSE--------
*
* where V stands for "valid pending ring index". Any number other
* than INVALID_PENDING_RING_IDX is OK. These entries are considered
* free and can contain any number other than
* INVALID_PENDING_RING_IDX. In practice we use 0.
*
* The in use non-INVALID_PENDING_RING_IDX (say 0, 5 and 9 in the
* above example) number is the index into pending_tx_info and
* mmap_pages arrays.
*/
struct pending_tx_info {
struct xen_netif_tx_request req; /* coalesced tx request */
pending_ring_idx_t head; /* head != INVALID_PENDING_RING_IDX
* if it is head of one or more tx
* reqs
*/
};
#define XEN_NETIF_TX_RING_SIZE __CONST_RING_SIZE(xen_netif_tx, PAGE_SIZE)
#define XEN_NETIF_RX_RING_SIZE __CONST_RING_SIZE(xen_netif_rx, PAGE_SIZE)
struct xenvif_rx_meta {
int id;
int size;
int gso_size;
};
/* Discriminate from any valid pending_idx value. */
#define INVALID_PENDING_IDX 0xFFFF
#define MAX_BUFFER_OFFSET PAGE_SIZE
#define MAX_PENDING_REQS 256
struct xenvif {
/* Unique identifier for this interface. */
domid_t domid;
unsigned int handle;
/* Reference to netback processing backend. */
struct xen_netbk *netbk;
u8 fe_dev_addr[6];
/* Use NAPI for guest TX */
struct napi_struct napi;
/* 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;
/* The shared rings and indexes. */
struct xen_netif_tx_back_ring tx;
struct sk_buff_head tx_queue;
struct page *mmap_pages[MAX_PENDING_REQS];
pending_ring_idx_t pending_prod;
pending_ring_idx_t pending_cons;
u16 pending_ring[MAX_PENDING_REQS];
struct pending_tx_info pending_tx_info[MAX_PENDING_REQS];
/* Coalescing tx requests before copying makes number of grant
* copy ops greater or equal to number of slots required. In
* worst case a tx request consumes 2 gnttab_copy.
*/
struct gnttab_copy tx_copy_ops[2*MAX_PENDING_REQS];
/* Use kthread for guest RX */
struct task_struct *task;
wait_queue_head_t wq;
/* When feature-split-event-channels = 0, tx_irq = rx_irq. */
unsigned int rx_irq;
/* Only used when feature-split-event-channels = 1 */
char rx_irq_name[IFNAMSIZ+4]; /* DEVNAME-rx */
struct xen_netif_rx_back_ring rx;
struct sk_buff_head rx_queue;
/* Allow xenvif_start_xmit() to peek ahead in the rx request
* ring. This is a prediction of what rx_req_cons will be
* once all queued skbs are put on the ring.
*/
RING_IDX rx_req_cons_peek;
/* Given MAX_BUFFER_OFFSET of 4096 the worst case is that each
* head/fragment page uses 2 copy operations because it
* straddles two buffers in the frontend.
*/
struct gnttab_copy grant_copy_op[2*XEN_NETIF_RX_RING_SIZE];
struct xenvif_rx_meta meta[2*XEN_NETIF_RX_RING_SIZE];
u8 fe_dev_addr[6];
/* Frontend feature information. */
u8 can_sg:1;
@ -80,13 +158,6 @@ struct xenvif {
/* Internal feature information. */
u8 can_queue:1; /* can queue packets for receiver? */
/*
* Allow xenvif_start_xmit() to peek ahead in the rx request
* ring. This is a prediction of what rx_req_cons will be
* once all queued skbs are put on the ring.
*/
RING_IDX rx_req_cons_peek;
/* Transmit shaping: allow 'credit_bytes' every 'credit_usec'. */
unsigned long credit_bytes;
unsigned long credit_usec;
@ -97,11 +168,7 @@ struct xenvif {
unsigned long rx_gso_checksum_fixup;
/* Miscellaneous private stuff. */
struct list_head schedule_list;
atomic_t refcnt;
struct net_device *dev;
wait_queue_head_t waiting_to_free;
};
static inline struct xenbus_device *xenvif_to_xenbus_device(struct xenvif *vif)
@ -109,9 +176,6 @@ static inline struct xenbus_device *xenvif_to_xenbus_device(struct xenvif *vif)
return to_xenbus_device(vif->dev->dev.parent);
}
#define XEN_NETIF_TX_RING_SIZE __CONST_RING_SIZE(xen_netif_tx, PAGE_SIZE)
#define XEN_NETIF_RX_RING_SIZE __CONST_RING_SIZE(xen_netif_rx, PAGE_SIZE)
struct xenvif *xenvif_alloc(struct device *parent,
domid_t domid,
unsigned int handle);
@ -121,39 +185,26 @@ int xenvif_connect(struct xenvif *vif, unsigned long tx_ring_ref,
unsigned int rx_evtchn);
void xenvif_disconnect(struct xenvif *vif);
void xenvif_get(struct xenvif *vif);
void xenvif_put(struct xenvif *vif);
int xenvif_xenbus_init(void);
void xenvif_xenbus_fini(void);
int xenvif_schedulable(struct xenvif *vif);
int xen_netbk_rx_ring_full(struct xenvif *vif);
int xenvif_rx_ring_full(struct xenvif *vif);
int xen_netbk_must_stop_queue(struct xenvif *vif);
int xenvif_must_stop_queue(struct xenvif *vif);
/* (Un)Map communication rings. */
void xen_netbk_unmap_frontend_rings(struct xenvif *vif);
int xen_netbk_map_frontend_rings(struct xenvif *vif,
grant_ref_t tx_ring_ref,
grant_ref_t rx_ring_ref);
/* (De)Register a xenvif with the netback backend. */
void xen_netbk_add_xenvif(struct xenvif *vif);
void xen_netbk_remove_xenvif(struct xenvif *vif);
/* (De)Schedule backend processing for a xenvif */
void xen_netbk_schedule_xenvif(struct xenvif *vif);
void xen_netbk_deschedule_xenvif(struct xenvif *vif);
void xenvif_unmap_frontend_rings(struct xenvif *vif);
int xenvif_map_frontend_rings(struct xenvif *vif,
grant_ref_t tx_ring_ref,
grant_ref_t rx_ring_ref);
/* Check for SKBs from frontend and schedule backend processing */
void xen_netbk_check_rx_xenvif(struct xenvif *vif);
/* Receive an SKB from the frontend */
void xenvif_receive_skb(struct xenvif *vif, struct sk_buff *skb);
void xenvif_check_rx_xenvif(struct xenvif *vif);
/* Queue an SKB for transmission to the frontend */
void xen_netbk_queue_tx_skb(struct xenvif *vif, struct sk_buff *skb);
void xenvif_queue_tx_skb(struct xenvif *vif, struct sk_buff *skb);
/* Notify xenvif that ring now has space to send an skb to the frontend */
void xenvif_notify_tx_completion(struct xenvif *vif);
@ -161,7 +212,12 @@ void xenvif_notify_tx_completion(struct xenvif *vif);
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);
unsigned int xenvif_count_skb_slots(struct xenvif *vif, struct sk_buff *skb);
int xenvif_tx_action(struct xenvif *vif, int budget);
void xenvif_rx_action(struct xenvif *vif);
int xenvif_kthread(void *data);
extern bool separate_tx_rx_irq;

135
drivers/net/xen-netback/interface.c
View File

@ -30,6 +30,7 @@
#include "common.h"
#include <linux/kthread.h>
#include <linux/ethtool.h>
#include <linux/rtnetlink.h>
#include <linux/if_vlan.h>
@ -38,17 +39,7 @@
#include <asm/xen/hypercall.h>
#define XENVIF_QUEUE_LENGTH 32
void xenvif_get(struct xenvif *vif)
{
atomic_inc(&vif->refcnt);
}
void xenvif_put(struct xenvif *vif)
{
if (atomic_dec_and_test(&vif->refcnt))
wake_up(&vif->waiting_to_free);
}
#define XENVIF_NAPI_WEIGHT 64
int xenvif_schedulable(struct xenvif *vif)
{
@ -57,28 +48,62 @@ int xenvif_schedulable(struct xenvif *vif)
static int xenvif_rx_schedulable(struct xenvif *vif)
{
return xenvif_schedulable(vif) && !xen_netbk_rx_ring_full(vif);
return xenvif_schedulable(vif) && !xenvif_rx_ring_full(vif);
}
static irqreturn_t xenvif_tx_interrupt(int irq, void *dev_id)
{
struct xenvif *vif = dev_id;
if (vif->netbk == NULL)
return IRQ_HANDLED;
xen_netbk_schedule_xenvif(vif);
if (RING_HAS_UNCONSUMED_REQUESTS(&vif->tx))
napi_schedule(&vif->napi);
return IRQ_HANDLED;
}
static int xenvif_poll(struct napi_struct *napi, int budget)
{
struct xenvif *vif = container_of(napi, struct xenvif, napi);
int work_done;
work_done = xenvif_tx_action(vif, budget);
if (work_done < budget) {
int more_to_do = 0;
unsigned long flags;
/* It is necessary to disable IRQ before calling
* RING_HAS_UNCONSUMED_REQUESTS. Otherwise we might
* lose event from the frontend.
*
* Consider:
* RING_HAS_UNCONSUMED_REQUESTS
* <frontend generates event to trigger napi_schedule>
* __napi_complete
*
* This handler is still in scheduled state so the
* event has no effect at all. After __napi_complete
* this handler is descheduled and cannot get
* scheduled again. We lose event in this case and the ring
* will be completely stalled.
*/
local_irq_save(flags);
RING_FINAL_CHECK_FOR_REQUESTS(&vif->tx, more_to_do);
if (!more_to_do)
__napi_complete(napi);
local_irq_restore(flags);
}
return work_done;
}
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);
@ -99,7 +124,8 @@ static int xenvif_start_xmit(struct sk_buff *skb, struct net_device *dev)
BUG_ON(skb->dev != dev);
if (vif->netbk == NULL)
/* Drop the packet if vif is not ready */
if (vif->task == NULL)
goto drop;
/* Drop the packet if the target domain has no receive buffers. */
@ -107,13 +133,12 @@ static int xenvif_start_xmit(struct sk_buff *skb, struct net_device *dev)
goto drop;
/* Reserve ring slots for the worst-case number of fragments. */
vif->rx_req_cons_peek += xen_netbk_count_skb_slots(vif, skb);
xenvif_get(vif);
vif->rx_req_cons_peek += xenvif_count_skb_slots(vif, skb);
if (vif->can_queue && xen_netbk_must_stop_queue(vif))
if (vif->can_queue && xenvif_must_stop_queue(vif))
netif_stop_queue(dev);
xen_netbk_queue_tx_skb(vif, skb);
xenvif_queue_tx_skb(vif, skb);
return NETDEV_TX_OK;
@ -123,11 +148,6 @@ static int xenvif_start_xmit(struct sk_buff *skb, struct net_device *dev)
return NETDEV_TX_OK;
}
void xenvif_receive_skb(struct xenvif *vif, struct sk_buff *skb)
{
netif_rx_ni(skb);
}
void xenvif_notify_tx_completion(struct xenvif *vif)
{
if (netif_queue_stopped(vif->dev) && xenvif_rx_schedulable(vif))
@ -142,21 +162,20 @@ static struct net_device_stats *xenvif_get_stats(struct net_device *dev)
static void xenvif_up(struct xenvif *vif)
{
xen_netbk_add_xenvif(vif);
napi_enable(&vif->napi);
enable_irq(vif->tx_irq);
if (vif->tx_irq != vif->rx_irq)
enable_irq(vif->rx_irq);
xen_netbk_check_rx_xenvif(vif);
xenvif_check_rx_xenvif(vif);
}
static void xenvif_down(struct xenvif *vif)
{
napi_disable(&vif->napi);
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);
}
static int xenvif_open(struct net_device *dev)
@ -272,11 +291,12 @@ struct xenvif *xenvif_alloc(struct device *parent, domid_t domid,
struct net_device *dev;
struct xenvif *vif;
char name[IFNAMSIZ] = {};
int i;
snprintf(name, IFNAMSIZ - 1, "vif%u.%u", domid, handle);
dev = alloc_netdev(sizeof(struct xenvif), name, ether_setup);
if (dev == NULL) {
pr_warn("Could not allocate netdev\n");
pr_warn("Could not allocate netdev for %s\n", name);
return ERR_PTR(-ENOMEM);
}
@ -285,14 +305,9 @@ struct xenvif *xenvif_alloc(struct device *parent, domid_t domid,
vif = netdev_priv(dev);
vif->domid = domid;
vif->handle = handle;
vif->netbk = NULL;
vif->can_sg = 1;
vif->csum = 1;
atomic_set(&vif->refcnt, 1);
init_waitqueue_head(&vif->waiting_to_free);
vif->dev = dev;
INIT_LIST_HEAD(&vif->schedule_list);
INIT_LIST_HEAD(&vif->notify_list);
vif->credit_bytes = vif->remaining_credit = ~0UL;
vif->credit_usec = 0UL;
@ -307,6 +322,16 @@ struct xenvif *xenvif_alloc(struct device *parent, domid_t domid,
dev->tx_queue_len = XENVIF_QUEUE_LENGTH;
skb_queue_head_init(&vif->rx_queue);
skb_queue_head_init(&vif->tx_queue);
vif->pending_cons = 0;
vif->pending_prod = MAX_PENDING_REQS;
for (i = 0; i < MAX_PENDING_REQS; i++)
vif->pending_ring[i] = i;
for (i = 0; i < MAX_PENDING_REQS; i++)
vif->mmap_pages[i] = NULL;
/*
* Initialise a dummy MAC address. We choose the numerically
* largest non-broadcast address to prevent the address getting
@ -316,6 +341,8 @@ struct xenvif *xenvif_alloc(struct device *parent, domid_t domid,
memset(dev->dev_addr, 0xFF, ETH_ALEN);
dev->dev_addr[0] &= ~0x01;
netif_napi_add(dev, &vif->napi, xenvif_poll, XENVIF_NAPI_WEIGHT);
netif_carrier_off(dev);
err = register_netdev(dev);
@ -341,7 +368,7 @@ int xenvif_connect(struct xenvif *vif, unsigned long tx_ring_ref,
__module_get(THIS_MODULE);
err = xen_netbk_map_frontend_rings(vif, tx_ring_ref, rx_ring_ref);
err = xenvif_map_frontend_rings(vif, tx_ring_ref, rx_ring_ref);
if (err < 0)
goto err;
@ -377,7 +404,14 @@ int xenvif_connect(struct xenvif *vif, unsigned long tx_ring_ref,
disable_irq(vif->rx_irq);
}
xenvif_get(vif);
init_waitqueue_head(&vif->wq);
vif->task = kthread_create(xenvif_kthread,
(void *)vif, vif->dev->name);
if (IS_ERR(vif->task)) {
pr_warn("Could not allocate kthread for %s\n", vif->dev->name);
err = PTR_ERR(vif->task);
goto err_rx_unbind;
}
rtnl_lock();
if (!vif->can_sg && vif->dev->mtu > ETH_DATA_LEN)
@ -388,12 +422,18 @@ int xenvif_connect(struct xenvif *vif, unsigned long tx_ring_ref,
xenvif_up(vif);
rtnl_unlock();
wake_up_process(vif->task);
return 0;
err_rx_unbind:
unbind_from_irqhandler(vif->rx_irq, vif);
vif->rx_irq = 0;
err_tx_unbind:
unbind_from_irqhandler(vif->tx_irq, vif);
vif->tx_irq = 0;
err_unmap:
xen_netbk_unmap_frontend_rings(vif);
xenvif_unmap_frontend_rings(vif);
err:
module_put(THIS_MODULE);
return err;
@ -408,7 +448,6 @@ void xenvif_carrier_off(struct xenvif *vif)
if (netif_running(dev))
xenvif_down(vif);
rtnl_unlock();
xenvif_put(vif);
}
void xenvif_disconnect(struct xenvif *vif)
@ -422,9 +461,6 @@ void xenvif_disconnect(struct xenvif *vif)
if (netif_carrier_ok(vif->dev))
xenvif_carrier_off(vif);
atomic_dec(&vif->refcnt);
wait_event(vif->waiting_to_free, atomic_read(&vif->refcnt) == 0);
if (vif->tx_irq) {
if (vif->tx_irq == vif->rx_irq)
unbind_from_irqhandler(vif->tx_irq, vif);
@ -438,9 +474,14 @@ void xenvif_disconnect(struct xenvif *vif)
need_module_put = 1;
}
if (vif->task)
kthread_stop(vif->task);
netif_napi_del(&vif->napi);
unregister_netdev(vif->dev);
xen_netbk_unmap_frontend_rings(vif);
xenvif_unmap_frontend_rings(vif);
free_netdev(vif->dev);

837
drivers/net/xen-netback/netback.c
View File

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