| Message ID | 1483075251-6889-4-git-send-email-jasowang@redhat.com |
|---|---|
| State | Changes Requested, archived |
| Delegated to: | David Miller |
| Headers | show |
From: Jason Wang <jasowang@redhat.com> Date: Fri, 30 Dec 2016 13:20:51 +0800 > @@ -1283,10 +1314,15 @@ static ssize_t tun_get_user(struct tun_struct *tun, struct tun_file *tfile, > skb_probe_transport_header(skb, 0); > > rxhash = skb_get_hash(skb); > + > #ifndef CONFIG_4KSTACKS > - local_bh_disable(); > - netif_receive_skb(skb); > - local_bh_enable(); > + if (!rx_batched) { > + local_bh_disable(); > + netif_receive_skb(skb); > + local_bh_enable(); > + } else { > + tun_rx_batched(tfile, skb, more); > + } > #else > netif_rx_ni(skb); > #endif If rx_batched has been set, and we are talking to clients not using this new MSG_MORE facility (or such clients don't have multiple TX packets to send to you, thus MSG_MORE is often clear), you are doing a lot more work per-packet than the existing code. You take the queue lock, you test state, you splice into a local queue on the stack, then you walk that local stack queue to submit just one SKB to netif_receive_skb(). I think you want to streamline this sequence in such cases so that the cost before and after is similar if not equivalent.
On Fri, 30 Dec 2016 13:20:51 +0800 Jason Wang <jasowang@redhat.com> wrote: > diff --git a/drivers/net/tun.c b/drivers/net/tun.c > index cd8e02c..a268ed9 100644 > --- a/drivers/net/tun.c > +++ b/drivers/net/tun.c > @@ -75,6 +75,10 @@ > > #include <linux/uaccess.h> > > +static int rx_batched; > +module_param(rx_batched, int, 0444); > +MODULE_PARM_DESC(rx_batched, "Number of packets batched in rx"); > + > /* Uncomment to enable debugging */ I like the concept or rx batching. But controlling it via a module parameter is one of the worst API choices. Ethtool would be better to use because that is how other network devices control batching. If you do ethtool, you could even extend it to have an number of packets and max latency value.
On 2017年01月01日 01:31, David Miller wrote: > From: Jason Wang <jasowang@redhat.com> > Date: Fri, 30 Dec 2016 13:20:51 +0800 > >> @@ -1283,10 +1314,15 @@ static ssize_t tun_get_user(struct tun_struct *tun, struct tun_file *tfile, >> skb_probe_transport_header(skb, 0); >> >> rxhash = skb_get_hash(skb); >> + >> #ifndef CONFIG_4KSTACKS >> - local_bh_disable(); >> - netif_receive_skb(skb); >> - local_bh_enable(); >> + if (!rx_batched) { >> + local_bh_disable(); >> + netif_receive_skb(skb); >> + local_bh_enable(); >> + } else { >> + tun_rx_batched(tfile, skb, more); >> + } >> #else >> netif_rx_ni(skb); >> #endif > If rx_batched has been set, and we are talking to clients not using > this new MSG_MORE facility (or such clients don't have multiple TX > packets to send to you, thus MSG_MORE is often clear), you are doing a > lot more work per-packet than the existing code. > > You take the queue lock, you test state, you splice into a local queue > on the stack, then you walk that local stack queue to submit just one > SKB to netif_receive_skb(). > > I think you want to streamline this sequence in such cases so that the > cost before and after is similar if not equivalent. Yes, so I will do a skb_queue_empty() check if !MSG_MORE and call netif_receive_skb() immediately in this case. This can save the wasted efforts. Thanks
On 2017年01月01日 05:03, Stephen Hemminger wrote: > On Fri, 30 Dec 2016 13:20:51 +0800 > Jason Wang <jasowang@redhat.com> wrote: > >> diff --git a/drivers/net/tun.c b/drivers/net/tun.c >> index cd8e02c..a268ed9 100644 >> --- a/drivers/net/tun.c >> +++ b/drivers/net/tun.c >> @@ -75,6 +75,10 @@ >> >> #include <linux/uaccess.h> >> >> +static int rx_batched; >> +module_param(rx_batched, int, 0444); >> +MODULE_PARM_DESC(rx_batched, "Number of packets batched in rx"); >> + >> /* Uncomment to enable debugging */ > I like the concept or rx batching. But controlling it via a module parameter > is one of the worst API choices. Ethtool would be better to use because that is > how other network devices control batching. > > If you do ethtool, you could even extend it to have an number of packets > and max latency value. Right, this is better (I believe you mean rx-frames). For rx-usecs, we could do it on top in the future. Thanks
diff --git a/drivers/net/tun.c b/drivers/net/tun.c index cd8e02c..a268ed9 100644 --- a/drivers/net/tun.c +++ b/drivers/net/tun.c @@ -75,6 +75,10 @@ #include <linux/uaccess.h> +static int rx_batched; +module_param(rx_batched, int, 0444); +MODULE_PARM_DESC(rx_batched, "Number of packets batched in rx"); + /* Uncomment to enable debugging */ /* #define TUN_DEBUG 1 */ @@ -522,6 +526,7 @@ static void tun_queue_purge(struct tun_file *tfile) while ((skb = skb_array_consume(&tfile->tx_array)) != NULL) kfree_skb(skb); + skb_queue_purge(&tfile->sk.sk_write_queue); skb_queue_purge(&tfile->sk.sk_error_queue); } @@ -1140,10 +1145,36 @@ static struct sk_buff *tun_alloc_skb(struct tun_file *tfile, return skb; } +static void tun_rx_batched(struct tun_file *tfile, struct sk_buff *skb, + int more) +{ + struct sk_buff_head *queue = &tfile->sk.sk_write_queue; + struct sk_buff_head process_queue; + int qlen; + bool rcv = false; + + spin_lock(&queue->lock); + qlen = skb_queue_len(queue); + __skb_queue_tail(queue, skb); + if (!more || qlen == rx_batched) { + __skb_queue_head_init(&process_queue); + skb_queue_splice_tail_init(queue, &process_queue); + rcv = true; + } + spin_unlock(&queue->lock); + + if (rcv) { + local_bh_disable(); + while ((skb = __skb_dequeue(&process_queue))) + netif_receive_skb(skb); + local_bh_enable(); + } +} + /* Get packet from user space buffer */ static ssize_t tun_get_user(struct tun_struct *tun, struct tun_file *tfile, void *msg_control, struct iov_iter *from, - int noblock) + int noblock, bool more) { struct tun_pi pi = { 0, cpu_to_be16(ETH_P_IP) }; struct sk_buff *skb; @@ -1283,10 +1314,15 @@ static ssize_t tun_get_user(struct tun_struct *tun, struct tun_file *tfile, skb_probe_transport_header(skb, 0); rxhash = skb_get_hash(skb); + #ifndef CONFIG_4KSTACKS - local_bh_disable(); - netif_receive_skb(skb); - local_bh_enable(); + if (!rx_batched) { + local_bh_disable(); + netif_receive_skb(skb); + local_bh_enable(); + } else { + tun_rx_batched(tfile, skb, more); + } #else netif_rx_ni(skb); #endif @@ -1312,7 +1348,8 @@ static ssize_t tun_chr_write_iter(struct kiocb *iocb, struct iov_iter *from) if (!tun) return -EBADFD; - result = tun_get_user(tun, tfile, NULL, from, file->f_flags & O_NONBLOCK); + result = tun_get_user(tun, tfile, NULL, from, + file->f_flags & O_NONBLOCK, false); tun_put(tun); return result; @@ -1570,7 +1607,8 @@ static int tun_sendmsg(struct socket *sock, struct msghdr *m, size_t total_len) return -EBADFD; ret = tun_get_user(tun, tfile, m->msg_control, &m->msg_iter, - m->msg_flags & MSG_DONTWAIT); + m->msg_flags & MSG_DONTWAIT, + m->msg_flags & MSG_MORE); tun_put(tun); return ret; }
We can only process 1 packet at one time during sendmsg(). This often lead bad cache utilization under heavy load. So this patch tries to do some batching during rx before submitting them to host network stack. This is done through accepting MSG_MORE as a hint from sendmsg() caller, if it was set, batch the packet temporarily in a linked list and submit them all once MSG_MORE were cleared. Tests were done by pktgen (burst=128) in guest over mlx4(noqueue) on host: Mpps -+% rx_batched=0 0.90 +0% rx_batched=4 0.97 +7.8% rx_batched=8 0.97 +7.8% rx_batched=16 0.98 +8.9% rx_batched=32 1.03 +14.4% rx_batched=48 1.09 +21.1% rx_batched=64 1.02 +13.3% The maximum number of batched packets were specified through a module parameter. Signed-off-by: Jason Wang <jasowang@redhat.com> --- drivers/net/tun.c | 50 ++++++++++++++++++++++++++++++++++++++++++++------ 1 file changed, 44 insertions(+), 6 deletions(-)