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Diffstat (limited to 'Documentation/networking/device_drivers/ethernet/amazon/ena.rst')
| -rw-r--r-- | Documentation/networking/device_drivers/ethernet/amazon/ena.rst | 32 |
1 files changed, 32 insertions, 0 deletions
diff --git a/Documentation/networking/device_drivers/ethernet/amazon/ena.rst b/Documentation/networking/device_drivers/ethernet/amazon/ena.rst index 8bcb173e0353..491492677632 100644 --- a/Documentation/networking/device_drivers/ethernet/amazon/ena.rst +++ b/Documentation/networking/device_drivers/ethernet/amazon/ena.rst @@ -205,6 +205,7 @@ Adaptive coalescing can be switched on/off through `ethtool(8)`'s More information about Adaptive Interrupt Moderation (DIM) can be found in Documentation/networking/net_dim.rst +.. _`RX copybreak`: RX copybreak ============ The rx_copybreak is initialized by default to ENA_DEFAULT_RX_COPYBREAK @@ -315,3 +316,34 @@ Rx - The new SKB is updated with the necessary information (protocol, checksum hw verify result, etc), and then passed to the network stack, using the NAPI interface function :code:`napi_gro_receive()`. + +Dynamic RX Buffers (DRB) +------------------------ + +Each RX descriptor in the RX ring is a single memory page (which is either 4KB +or 16KB long depending on system's configurations). +To reduce the memory allocations required when dealing with a high rate of small +packets, the driver tries to reuse the remaining RX descriptor's space if more +than 2KB of this page remain unused. + +A simple example of this mechanism is the following sequence of events: + +:: + + 1. Driver allocates page-sized RX buffer and passes it to hardware + +----------------------+ + |4KB RX Buffer | + +----------------------+ + + 2. A 300Bytes packet is received on this buffer + + 3. The driver increases the ref count on this page and returns it back to + HW as an RX buffer of size 4KB - 300Bytes = 3796 Bytes + +----+--------------------+ + |****|3796 Bytes RX Buffer| + +----+--------------------+ + +This mechanism isn't used when an XDP program is loaded, or when the +RX packet is less than rx_copybreak bytes (in which case the packet is +copied out of the RX buffer into the linear part of a new skb allocated +for it and the RX buffer remains the same size, see `RX copybreak`_). |