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| -rw-r--r-- | Documentation/networking/scaling.rst | 12 |
1 files changed, 8 insertions, 4 deletions
diff --git a/Documentation/networking/scaling.rst b/Documentation/networking/scaling.rst index 99b6a61e5e31..0023afa530ec 100644 --- a/Documentation/networking/scaling.rst +++ b/Documentation/networking/scaling.rst @@ -38,11 +38,15 @@ that is not the focus of these techniques. The filter used in RSS is typically a hash function over the network and/or transport layer headers-- for example, a 4-tuple hash over IP addresses and TCP ports of a packet. The most common hardware -implementation of RSS uses a 128-entry indirection table where each entry +implementation of RSS uses an indirection table where each entry stores a queue number. The receive queue for a packet is determined -by masking out the low order seven bits of the computed hash for the -packet (usually a Toeplitz hash), taking this number as a key into the -indirection table and reading the corresponding value. +by indexing the indirection table with the low order bits of the +computed hash for the packet (usually a Toeplitz hash). + +The indirection table helps even out the traffic distribution when queue +count is not a power of two. NICs should provide an indirection table +at least 4 times larger than the queue count. 4x table results in ~16% +imbalance between the queues, which is acceptable for most applications. Some NICs support symmetric RSS hashing where, if the IP (source address, destination address) and TCP/UDP (source port, destination port) tuples |