Hi ,Kyle Larose&Jingjing

-----Original Message-----
From: Kyle Larose [mailto:eomereadig@gmail.com]
Sent: Wednesday, August 3, 2016 12:22 AM
To: Zhao1, Wei <redacted>
Cc: Wu, Jingjing <redacted>; dev@dpdk.org
Subject: Re: [dpdk-dev] [PATCH v2] net/i40e: fix Rx statistic inconsistent

Hello Wei,


On Tue, Aug 2, 2016 at 2:59 AM, Zhao1, Wei [off-list ref] wrote:

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Hi, Wujingjing and Kyle Larose

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-----Original Message-----
From: Zhao1, Wei
Sent: Tuesday, August 2, 2016 11:27 AM
To: Wu, Jingjing <redacted>; Lu, Wenzhuo
[off-list ref]
Cc: dev@dpdk.org
Subject: RE: [dpdk-dev] [PATCH v2] net/i40e: fix Rx statistic
inconsistent

Hi,Wu jingjing and wenzhuo

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-----Original Message-----
From: Zhao1, Wei
Sent: Monday, August 1, 2016 4:58 PM
To: 'Kyle Larose' <redacted>
Cc: dev@dpdk.org
Subject: RE: [dpdk-dev] [PATCH v2] net/i40e: fix Rx statistic
inconsistent

Hi, Kyle Larose
   The core problem is i40e has no statistic of discard bytes, that
means even if when ports are not stopped, the statistic
rx_good_bytes is consist of discard
bytes，is that reasonable? In other words, I can just minus discard
bytes from rx_good_bytes if I can get discard bytes number, that is
much

better.

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-----Original Message-----
From: Kyle Larose [mailto:eomereadig@gmail.com]
Sent: Saturday, July 30, 2016 1:17 AM
To: Zhao1, Wei <redacted>
Cc: dev@dpdk.org
Subject: Re: [dpdk-dev] [PATCH v2] net/i40e: fix Rx statistic
inconsistent

On Fri, Jul 29, 2016 at 4:50 AM, Wei Zhao1 [off-list ref]

wrote:

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rx_good_bytes and rx_good_packets statistic is inconsistent when
port stopped,ipackets statistic is minus the discard packets but
rx_bytes statistic not.Also,i40e has no statistic of discard
bytes, so we have to delete discard packets item from

rx_good_packets statistic.

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Fixes: 9aace75fc82e ("i40e: fix statistics")

Signed-off-by: Wei Zhao1 <redacted>
---
 drivers/net/i40e/i40e_ethdev.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/drivers/net/i40e/i40e_ethdev.c

b/drivers/net/i40e/i40e_ethdev.c index 11a5804..553dfd9 100644

--- a/drivers/net/i40e/i40e_ethdev.c
+++ b/drivers/net/i40e/i40e_ethdev.c

@@ -2319,8 +2319,7 @@ i40e_dev_stats_get(struct rte_eth_dev

*dev,

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struct rte_eth_stats *stats)

        stats->ipackets = pf->main_vsi->eth_stats.rx_unicast +
                        pf->main_vsi->eth_stats.rx_multicast +
-                       pf->main_vsi->eth_stats.rx_broadcast -
-                       pf->main_vsi->eth_stats.rx_discards;
+                       pf->main_vsi->eth_stats.rx_broadcast;
        stats->opackets = pf->main_vsi->eth_stats.tx_unicast +
                        pf->main_vsi->eth_stats.tx_multicast +
                        pf->main_vsi->eth_stats.tx_broadcast;
--
2.5.5

Is it not worse to report a received packet when no packet was
actually received by the upper layers under normal operations than
to ensure that packets and  bytes are consistent when an interface
is stopped? It seems like the first case is much more likely to
occur than the

second.

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Are we just introducing a new issue to fix another?

How does this behaviour compare to other NICs? Does the ixgbe
report discarded packets in its ipackets? My reading of the driver is that

it does not.

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In fact, it does something interesting to deal with the
problem:

from:
http://dpdk.org/browse/dpdk/tree/drivers/net/ixgbe/ixgbe_ethdev.c

/*
* An errata states that gprc actually counts good + missed packets:
* Workaround to set gprc to summated queue packet receives */
hw_stats-

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gprc = *total_qprc;

total_gprc is equal to the sum of the qprc per queue. Can we do
something similar on the i40e instead of adding unicast, mulitcast
and

broadcast?


I have checked ixgbe code about  Rx statistic, in function
ixgbe_read_stats_registers() we can find the rx_good_bytes and
rx_good_packets statistic.
It is listed below, we  can see rx_good_packets is also just addition
of Queue Packets Received Count and  not minused  discard packet

number.

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Is there some wrong of understanding?

My understanding of the problem can be broken into three parts:
 1) In Unicast/Multicast/Broadcast packet counters are counting packets
which were discarded
 2) The corresponding byte counters count packets which were discarded.
 3) There are no discarded byte counters.

Our in bytes counter consists of the sum of in unicast, in multicast, and in
broadcast. This sum includes discarded bytes, which we do not want, for two
reasons. First, it would lead to misleading bitrate
reports: people expect to see the amount of traffic actually handled.
Second, it conflicts with the current packet counters (the counters without
your change).

Obviously if we could count the discarded bytes, we could subtract them.
Alternatively, if we could count only received bytes which were not
discarded, then we would not need to subtract discarded bytes from the
received bytes counter. The ixgbe had a similar problem for packets, but
presumably not bytes. So, I looked to it for inspiration.

Presumably, the ixgbe per-queue counters count all received packets, per
queue, and do not count discarded packets.Thus, is you take the sum of
received packets across all queues, you can find the total number of received
packets without discards included.

Can we not do the same thing on the i40e, but for bytes? I just took a quick
look at the datasheet, and I cannot see anything offhand that is equivalent to
qbrc, which is what I would have used here. That said, I'm not an i40e expert,
so I may have missed something. That's why I'm asking if it's possible. :)

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for (i = 0; i < IXGBE_QUEUE_STAT_COUNTERS; i++) { ......
                                 *total_qprc += hw_stats->qprc[i];
              *total_qbrc += hw_stats->qbrc[i]; ......
}

   The problem is i40e has no statistic of discard bytes, so it is
impossible to minus discard bytes from rx_good_bytes . If you think it's not

reasonable to Delete  rx_discards iterm from rx_good_packets statistic, this
patch will be superseded. Because I didn't find other way to correct this
problem at present.

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I understand that there is no discard byte counter. Are there per-queue byte
counters on the i40e, which do not count discarded byte, with which we
could do a similar thing as the packet counters on the ixgbe?

My concern is that both solutions aside from that are not good: either we
count less packets received than bytes received, or we count discarded
packets as received packets. Is there any chance that a firmware update in
the future could fix this? This sort of inconsistency, or inability to provide
*good* stats, really sucks for a NIC.

Thanks,

Kyle

According to your suggestion and meeting last week with harry ,I have supply a v3 patch for this problem.
[dpdk-dev,v3] net/i40e: fix Rx statistic inconsistent  , Permalink :/dev/patchwork/patch/15161/.
This fix is avoiding  statistic work when port is stopped.