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
62 Some advanced NICs allow steering packets to queues based on
72 module parameter for specifying the number of hardware queues to
75 for each CPU if the device supports enough queues, or otherwise at least
81 default mapping is to distribute the queues evenly in the table, but the
84 indirection table could be done to give different queues different
95 of queues to IRQs can be determined from /proc/interrupts. By default,
110 is to allocate as many queues as there are CPUs in the system (or the
112 is likely the one with the smallest number of receive queues where no
120 initial tests, so limit the number of queues to the number of CPU cores
128 useful when application wants to constrain the set of queues receiving
131 to queues 0 and 1.
216   /sys/class/net/<dev>/queues/rx-<n>/rps_cpus
235 and unnecessary. If there are fewer hardware queues than CPUs, then
385   /sys/class/net/<dev>/queues/rx-<n>/rps_flow_cnt
402 queues. So for instance, if rps_sock_flow_entries is set to 32768 and there
403 are 16 configured receive queues, rps_flow_cnt for each queue might be
440 of CPU to queues is automatically deduced from the IRQ affinities
463 The goal of this mapping is usually to assign queues
465 these queues are processed on a CPU within this set. This choice
473 2. XPS using receive queues map
477 queues can be mapped to a set of transmit queues (many:many), although
494 CPUs/receive-queues that may use that queue to transmit. The reverse
495 mapping, from CPUs to transmit queues or from receive-queues to transmit
496 queues, is computed and maintained for each network device. When
503 queues match, one is selected by using the flow hash to compute an index
526 how, XPS is configured at device init. The mapping of CPUs/receive-queues
531   /sys/class/net/<dev>/queues/tx-<n>/xps_cpus
533 For selection based on receive-queues map::
535   /sys/class/net/<dev>/queues/tx-<n>/xps_rxqs
544 If there are as many queues as there are CPUs in the system, then each
546 experience no contention. If there are fewer queues than CPUs, then the
563   /sys/class/net/<dev>/queues/tx-<n>/tx_maxrate