[dpdk-dev,v3] docs: add statistics read frequency to fm10k guide
Commit Message
This patch documents that the statistics of fm10k based NICs must be
read regularly in order to avoid an undetected 32 bit integer-overflow.
Signed-off-by: Harry van Haaren <harry.van.haaren@intel.com>
Acked-by: John McNamara <john.mcnamara@intel.com>
---
v3:
-Removed paragraph from "Known Issues" based on feedback
v2:
-Moved notes to Known Issues section of Release Notes.
doc/guides/nics/fm10k.rst | 16 ++++++++++++++++
1 file changed, 16 insertions(+)
Comments
2016-03-08 17:16, Harry van Haaren:
> This patch documents that the statistics of fm10k based NICs must be
> read regularly in order to avoid an undetected 32 bit integer-overflow.
>
> Signed-off-by: Harry van Haaren <harry.van.haaren@intel.com>
> Acked-by: John McNamara <john.mcnamara@intel.com>
Applied, thanks
@@ -65,3 +65,19 @@ The FM10000 family of NICS support a maximum of a 15K jumbo frame. The value
is fixed and cannot be changed. So, even when the ``rxmode.max_rx_pkt_len``
member of ``struct rte_eth_conf`` is set to a value lower than 15364, frames
up to 15364 bytes can still reach the host interface.
+
+Statistic Polling Frequency
+~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The FM10000 NICs expose a set of statistics via the PCI BARs. These statistics
+are read from the hardware registers when ``rte_eth_stats_get()`` or
+``rte_eth_xstats_get()`` is called. The packet counting registers are 32 bits
+while the byte counting registers are 48 bits. As a result, the statistics must
+be polled regularly in order to ensure the consistency of the returned reads.
+
+Given the PCIe Gen3 x8, about 50Gbps of traffic can occur. With 64 byte packets
+this gives almost 100 million packets/second, causing 32 bit integer overflow
+after approx 40 seconds. To ensure these overflows are detected and accounted
+for in the statistics, it is necessary to read statistic regularly. It is
+suggested to read stats every 20 seconds, which will ensure the statistics
+are accurate.