Documentation/networking/scaling.rst

27 Contemporary NICs support multiple receive and transmit descriptor queues
29 queues to distribute processing among CPUs. The NIC distributes packets by
69 Some advanced NICs allow steering packets to queues based on
79 module parameter for specifying the number of hardware queues to
82 for each CPU if the device supports enough queues, or otherwise at least
88 default mapping is to distribute the queues evenly in the table, but the
91 indirection table could be done to give different queues different
102 of queues to IRQs can be determined from /proc/interrupts. By default,
117 is to allocate as many queues as there are CPUs in the system (or the
119 is likely the one with the smallest number of receive queues where no
127 initial tests, so limit the number of queues to the number of CPU cores
135 useful when application wants to constrain the set of queues receiving
138 to queues 0 and 1.
223   /sys/class/net/<dev>/queues/rx-<n>/rps_cpus
242 and unnecessary. If there are fewer hardware queues than CPUs, then
392   /sys/class/net/<dev>/queues/rx-<n>/rps_flow_cnt
409 queues. So for instance, if rps_sock_flow_entries is set to 32768 and there
410 are 16 configured receive queues, rps_flow_cnt for each queue might be
449 of CPU to queues is automatically deduced from the IRQ affinities
472 The goal of this mapping is usually to assign queues
474 these queues are processed on a CPU within this set. This choice
482 2. XPS using receive queues map
486 queues can be mapped to a set of transmit queues (many:many), although
503 CPUs/receive-queues that may use that queue to transmit. The reverse
504 mapping, from CPUs to transmit queues or from receive-queues to transmit
505 queues, is computed and maintained for each network device. When
512 queues match, one is selected by using the flow hash to compute an index
535 how, XPS is configured at device init. The mapping of CPUs/receive-queues
540   /sys/class/net/<dev>/queues/tx-<n>/xps_cpus
542 For selection based on receive-queues map::
544   /sys/class/net/<dev>/queues/tx-<n>/xps_rxqs
553 If there are as many queues as there are CPUs in the system, then each
555 experience no contention. If there are fewer queues than CPUs, then the
572   /sys/class/net/<dev>/queues/tx-<n>/tx_maxrate