Add a description for local page cache system to the ENA driver readme file.
Signed-off-by: Shay Agroskin <shay...@amazon.com> --- .../device_drivers/ethernet/amazon/ena.rst | 25 +++++++++++++++++++ 1 file changed, 25 insertions(+) diff --git a/Documentation/networking/device_drivers/ethernet/amazon/ena.rst b/Documentation/networking/device_drivers/ethernet/amazon/ena.rst index 3561a8a29fd2..d3423a2f472c 100644 --- a/Documentation/networking/device_drivers/ethernet/amazon/ena.rst +++ b/Documentation/networking/device_drivers/ethernet/amazon/ena.rst @@ -222,6 +222,31 @@ If the frame length is larger than rx_copybreak, napi_get_frags() is used, otherwise netdev_alloc_skb_ip_align() is used, the buffer content is copied (by CPU) to the SKB, and the buffer is recycled. +Local Page Cache (LPC) +====================== +ENA Linux driver allows to reduce lock contention and improve CPU usage by +allocating RX buffers from a page cache rather than from Linux memory system +(PCP or buddy allocator). The cache is created and binded per RX queue, and +pages allocated for the queue are stored in the cache (up to cache maximum +size). + +When enabled, LPC cache size is ENA_LPC_DEFAULT_MULTIPLIER * 1024 (2048 by +default) pages. + +The cache usage for each queue can be monitored using ``ethtool -S`` counters. Where: + +- *rx_queue#_lpc_warm_up* - number of pages that were allocated and stored in + the cache +- *rx_queue#_lpc_full* - number of pages that were allocated without using the + cache because it didn't have free pages +- *rx_queue#_lpc_wrong_numa* - number of pages from the cache that belong to a + different NUMA node than the CPU which runs the NAPI routine. In this case, + the driver would try to allocate a new page from the same NUMA node instead + +LPC is disabled when using XDP or when using less than 16 queue pairs. Note that +cache usage might increase the memory footprint of the driver (depending on the +traffic). + Statistics ========== The user can obtain ENA device and driver statistics using ethtool. -- 2.25.1
