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git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
kernel
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linux
docs: networking: mention that RSS table should be 4x the queue count
Spell out the recommendation that the RSS table should be
4x the queue count to avoid traffic imbalance. Include minor
rephrasing and removal of the explicit 128 entry example
since a 128 entry table is inadequate on modern machines.
Reviewed-by: Eric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20260131225454.1225151-2-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
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Documentation/networking/scaling.rst
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Documentation/networking/scaling.rst
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The filter used in RSS is typically a hash function over the network
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and/or transport layer headers-- for example, a 4-tuple hash over
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IP addresses and TCP ports of a packet. The most common hardware
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implementation of RSS uses a 128-entry indirection table where each entry
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implementation of RSS uses an indirection table where each entry
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stores a queue number. The receive queue for a packet is determined
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by masking out the low order seven bits of the computed hash for the
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packet (usually a Toeplitz hash), taking this number as a key into the
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indirection table and reading the corresponding value.
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by indexing the indirection table with the low order bits of the
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computed hash for the packet (usually a Toeplitz hash).
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The indirection table helps even out the traffic distribution when queue
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count is not a power of two. NICs should provide an indirection table
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at least 4 times larger than the queue count. 4x table results in ~16%
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imbalance between the queues, which is acceptable for most applications.
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Some NICs support symmetric RSS hashing where, if the IP (source address,
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destination address) and TCP/UDP (source port, destination port) tuples