[dpdk-dev] 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>
---
doc/guides/nics/fm10k.rst | 16 ++++++++++++++++
doc/guides/rel_notes/release_2_3.rst | 4 ++++
2 files changed, 20 insertions(+)
Comments
2016-02-08 15:42, 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>
> ---
> doc/guides/nics/fm10k.rst | 16 ++++++++++++++++
> doc/guides/rel_notes/release_2_3.rst | 4 ++++
Thanks for improving the doc.
I think we should not add it to the release notes. Other opinions?
> From: Thomas Monjalon [mailto:thomas.monjalon@6wind.com]
> 2016-02-08 15:42, 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>
> > ---
> > doc/guides/nics/fm10k.rst | 16 ++++++++++++++++
> > doc/guides/rel_notes/release_2_3.rst | 4 ++++
>
> Thanks for improving the doc.
> I think we should not add it to the release notes. Other opinions?
I was unsure on including it, and have no problem with it not being included. V2?
> -----Original Message-----
> From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Thomas Monjalon
> Sent: Monday, February 8, 2016 4:01 PM
> To: Van Haaren, Harry <harry.van.haaren@intel.com>
> Cc: dev@dpdk.org
> Subject: Re: [dpdk-dev] [PATCH] docs: add statistics read frequency to
> fm10k guide
>
> 2016-02-08 15:42, 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>
> > ---
> > doc/guides/nics/fm10k.rst | 16 ++++++++++++++++
> > doc/guides/rel_notes/release_2_3.rst | 4 ++++
>
> Thanks for improving the doc.
> I think we should not add it to the release notes. Other opinions?
In general it shouldn't be required to add a note about doc changes to the release note.
In this case the note part may make more sense in the "Known Issues" section of the release note.
John.
--
@@ -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 gaurantee the statistics
+are accurate.
@@ -15,6 +15,10 @@ EAL
Drivers
~~~~~~~
+* **FM10K: Statistics Polling Frequency**
+
+ A section has been added to the NIC guide for fm10k about the time
+ between reading statistics and 32 bit packet counter overflows.
Libraries
~~~~~~~~~