[dpdk-dev,v2] 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>
---
v2:
-Moved notes to Known Issues section of Release Notes.
doc/guides/nics/fm10k.rst | 16 ++++++++++++++++
doc/guides/rel_notes/release_2_3.rst | 4 ++++
2 files changed, 20 insertions(+)
Comments
> -----Original Message-----
> From: Van Haaren, Harry
> Sent: Tuesday, February 9, 2016 3:20 PM
> To: Chen, Jing D <jing.d.chen@intel.com>
> Cc: Mcnamara, John <john.mcnamara@intel.com>; dev@dpdk.org; Van Haaren,
> Harry <harry.van.haaren@intel.com>
> Subject: [PATCH v2] docs: add statistics read frequency to fm10k guide
>
> 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>
> Known Issues
> ------------
>
> +* **FM10K: Statistics Polling Frequency**
> +
> + A section has been added to the NIC guide for fm10k about the maximum
> + time between reading statistics and 32 bit packet counter overflows.
Hi Thomas,
We should probably call this section "New Known Issues" and then copy them to the legacy "Known Issues" doc after 1 release.
http://dpdk.org/doc/guides/rel_notes/release_2_2.html#known-issues
http://dpdk.org/doc/guides/rel_notes/known_issues.html
Or any other suggestion?
John
2016-02-22 17:18, Mcnamara, John:
> > Known Issues
> > ------------
> >
> > +* **FM10K: Statistics Polling Frequency**
> > +
> > + A section has been added to the NIC guide for fm10k about the maximum
> > + time between reading statistics and 32 bit packet counter overflows.
>
> Hi Thomas,
>
> We should probably call this section "New Known Issues" and then copy them to the legacy "Known Issues" doc after 1 release.
>
> http://dpdk.org/doc/guides/rel_notes/release_2_2.html#known-issues
> http://dpdk.org/doc/guides/rel_notes/known_issues.html
>
> Or any other suggestion?
Yes it is an option.
Or we can simply maintain known issues in one place and remove the
per-release section.
2016-02-09 15:19, Harry van Haaren:
> +suggested to read stats every 20 seconds, which will gaurantee the statistics
typo: gaurantee
> --- a/doc/guides/rel_notes/release_2_3.rst
> +++ b/doc/guides/rel_notes/release_2_3.rst
> @@ -31,6 +31,10 @@ Other
> Known Issues
> ------------
>
> +* **FM10K: Statistics Polling Frequency**
> +
> + A section has been added to the NIC guide for fm10k about the maximum
> + time between reading statistics and 32 bit packet counter overflows.
I don't think it is an issue. It is common to every counter registers.
It is good to give some explanations in the doc but I don't think it must be
registered as an issue.
@@ -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.
@@ -31,6 +31,10 @@ Other
Known Issues
------------
+* **FM10K: Statistics Polling Frequency**
+
+ A section has been added to the NIC guide for fm10k about the maximum
+ time between reading statistics and 32 bit packet counter overflows.
API Changes
-----------