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Diffstat (limited to 'Documentation/networking/multiqueue.txt')
| -rw-r--r-- | Documentation/networking/multiqueue.txt | 100 |
1 files changed, 32 insertions, 68 deletions
diff --git a/Documentation/networking/multiqueue.txt b/Documentation/networking/multiqueue.txt index ea5a42e8f79..4caa0e314cc 100644 --- a/Documentation/networking/multiqueue.txt +++ b/Documentation/networking/multiqueue.txt @@ -3,19 +3,11 @@ =========================================== Section 1: Base driver requirements for implementing multiqueue support -Section 2: Qdisc support for multiqueue devices -Section 3: Brief howto using PRIO or RR for multiqueue devices - Intro: Kernel support for multiqueue devices --------------------------------------------------------- -Kernel support for multiqueue devices is only an API that is presented to the -netdevice layer for base drivers to implement. This feature is part of the -core networking stack, and all network devices will be running on the -multiqueue-aware stack. If a base driver only has one queue, then these -changes are transparent to that driver. - +Kernel support for multiqueue devices is always present. Section 1: Base driver requirements for implementing multiqueue support ----------------------------------------------------------------------- @@ -32,84 +24,56 @@ netif_{start|stop|wake}_subqueue() functions to manage each queue while the device is still operational. netdev->queue_lock is still used when the device comes online or when it's completely shut down (unregister_netdev(), etc.). -Finally, the base driver should indicate that it is a multiqueue device. The -feature flag NETIF_F_MULTI_QUEUE should be added to the netdev->features -bitmap on device initialization. Below is an example from e1000: - -#ifdef CONFIG_E1000_MQ - if ( (adapter->hw.mac.type == e1000_82571) || - (adapter->hw.mac.type == e1000_82572) || - (adapter->hw.mac.type == e1000_80003es2lan)) - netdev->features |= NETIF_F_MULTI_QUEUE; -#endif - Section 2: Qdisc support for multiqueue devices ------------------------------------------------ -Currently two qdiscs support multiqueue devices. A new round-robin qdisc, -sch_rr, and sch_prio. The qdisc is responsible for classifying the skb's to -bands and queues, and will store the queue mapping into skb->queue_mapping. -Use this field in the base driver to determine which queue to send the skb -to. +----------------------------------------------- -sch_rr has been added for hardware that doesn't want scheduling policies from -software, so it's a straight round-robin qdisc. It uses the same syntax and -classification priomap that sch_prio uses, so it should be intuitive to -configure for people who've used sch_prio. +Currently two qdiscs are optimized for multiqueue devices. The first is the +default pfifo_fast qdisc. This qdisc supports one qdisc per hardware queue. +A new round-robin qdisc, sch_multiq also supports multiple hardware queues. The +qdisc is responsible for classifying the skb's and then directing the skb's to +bands and queues based on the value in skb->queue_mapping. Use this field in +the base driver to determine which queue to send the skb to. -In order to utilitize the multiqueue features of the qdiscs, the network -device layer needs to enable multiple queue support. This can be done by -selecting NETDEVICES_MULTIQUEUE under Drivers. +sch_multiq has been added for hardware that wishes to avoid head-of-line +blocking. It will cycle though the bands and verify that the hardware queue +associated with the band is not stopped prior to dequeuing a packet. -The PRIO qdisc naturally plugs into a multiqueue device. If -NETDEVICES_MULTIQUEUE is selected, then on qdisc load, the number of -bands requested is compared to the number of queues on the hardware. If they -are equal, it sets a one-to-one mapping up between the queues and bands. If -they're not equal, it will not load the qdisc. This is the same behavior -for RR. Once the association is made, any skb that is classified will have -skb->queue_mapping set, which will allow the driver to properly queue skb's -to multiple queues. +On qdisc load, the number of bands is based on the number of queues on the +hardware. Once the association is made, any skb with skb->queue_mapping set, +will be queued to the band associated with the hardware queue. -Section 3: Brief howto using PRIO and RR for multiqueue devices +Section 3: Brief howto using MULTIQ for multiqueue devices --------------------------------------------------------------- The userspace command 'tc,' part of the iproute2 package, is used to configure -qdiscs. To add the PRIO qdisc to your network device, assuming the device is -called eth0, run the following command: +qdiscs. To add the MULTIQ qdisc to your network device, assuming the device +is called eth0, run the following command: -# tc qdisc add dev eth0 root handle 1: prio bands 4 multiqueue +# tc qdisc add dev eth0 root handle 1: multiq -This will create 4 bands, 0 being highest priority, and associate those bands -to the queues on your NIC. Assuming eth0 has 4 Tx queues, the band mapping -would look like: +The qdisc will allocate the number of bands to equal the number of queues that +the device reports, and bring the qdisc online. Assuming eth0 has 4 Tx +queues, the band mapping would look like: band 0 => queue 0 band 1 => queue 1 band 2 => queue 2 band 3 => queue 3 -Traffic will begin flowing through each queue if your TOS values are assigning -traffic across the various bands. For example, ssh traffic will always try to -go out band 0 based on TOS -> Linux priority conversion (realtime traffic), -so it will be sent out queue 0. ICMP traffic (pings) fall into the "normal" -traffic classification, which is band 1. Therefore pings will be send out -queue 1 on the NIC. - -Note the use of the multiqueue keyword. This is only in versions of iproute2 -that support multiqueue networking devices; if this is omitted when loading -a qdisc onto a multiqueue device, the qdisc will load and operate the same -if it were loaded onto a single-queue device (i.e. - sends all traffic to -queue 0). - -Another alternative to multiqueue band allocation can be done by using the -multiqueue option and specify 0 bands. If this is the case, the qdisc will -allocate the number of bands to equal the number of queues that the device -reports, and bring the qdisc online. +Traffic will begin flowing through each queue based on either the simple_tx_hash +function or based on netdev->select_queue() if you have it defined. -The behavior of tc filters remains the same, where it will override TOS priority -classification. +The behavior of tc filters remains the same. However a new tc action, +skbedit, has been added. Assuming you wanted to route all traffic to a +specific host, for example 192.168.0.3, through a specific queue you could use +this action and establish a filter such as: +tc filter add dev eth0 parent 1: protocol ip prio 1 u32 \ + match ip dst 192.168.0.3 \ + action skbedit queue_mapping 3 -Author: Peter P. Waskiewicz Jr. <peter.p.waskiewicz.jr@intel.com> +Author: Alexander Duyck <alexander.h.duyck@intel.com> +Original Author: Peter P. Waskiewicz Jr. <peter.p.waskiewicz.jr@intel.com> |