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Date: Tue, 5 May 2009 23:24:31 +0200 (CEST)
From: Jesper Dangaard Brouer <hawk@...u.dk>
To: David Miller <davem@...emloft.net>
Cc: jeffrey.t.kirsher@...el.com, hawk@...x.dk,
netdev <netdev@...r.kernel.org>,
e1000-devel@...ts.sourceforge.net, jesse.brandeburg@...el.com,
bruce.w.allan@...el.com, peter.p.waskiewicz.jr@...el.com,
john.ronciak@...el.com
Subject: Re: [PATCH] igb: Record hardware RX overruns in net_stats
On Tue, 5 May 2009, David Miller wrote:
> From: Jeff Kirsher <jeffrey.t.kirsher@...el.com>
> Date: Tue, 5 May 2009 11:47:09 -0700
>
>> NAK. RNBC is not a counter for buffer overruns, and so should not be
>> counted as such.
>
> I'd say technically it is, it indicates that more packets arrived than
> the available receive buffers could handle.
I agree with DaveM. Technically it _is_ a buffer overflow, but in the host
memory not the NIC. I'm sort of pushing the system into a situation where
it cannot empty the receive buffers fast enough.
I can fairly easily provoke this situation by adding too many iptables
rules, which (intentionally) cause high CPU load and causes ksoftirqd to
run (I'm Oprofiling netfilter modules).
> If anything, this is the closest this device has for this kind of
> situation, and it's useful for diagnosing problems.
Its really useful for diagnosing problems, and I'm betting that this is a
real-life situation which people is going to experience. We might as well
help our self to more easily identify this issue when people report drop
problems.
Notice that I'm seeing:
rx_no_buffer_count: 136955
rx_missed_errors: 0
Thus, the rx_missed_errors is zero, which according to the datasheet is
the "real" fifo drop (the MPC register, Missed Packets Count) and PCI
bandwidth problem indications.
If we really should nitpick, then:
adapter->net_stats.rx_missed_errors = adapter->stats.mpc
Should then have been stored in the rx_fifo_errors. Notice that
rx_missed_errors is presented to userspace as drops (see
net/core/dev.c:2624).
I think that both MPC and RNBC should be stored in rx_fifo_errors (and of
cause still keeping them seperate to ethtool -S).
I'll post two patches with these changes tomorrow, for you evaluation.
Please reconsider you NAK.
Greetings,
Jesper Brouer
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