On 23.09.2014 19:46, Luigi Rizzo wrote:
On Tue, Sep 23, 2014 at 07:17:08PM +0400, Alexander V. Chernikov wrote:
On 23.09.2014 18:44, Luigi Rizzo wrote:
...
However, in addition to non-symmetric RSS (which is hopefully being
addressed), there is another
usual "producer - multuple consumers" problem: one snort process can
start process packets very slowly, or hang, or crash.
In that case host RX ring is getting full, NIC fails to push packets to
given queue and start storing them inside
its skid buffer (512k for Niantic afair). After that buffer becomes full
traffic and all processing stops.
interesting. Actually, scary!
Do you have any reference to the data sheets documenting
that behaviour ? I have indeed received reports saying something
Quoting latest 82599 datasheet:
Flow control:
3.7.7.3.4 Packet Buffer Size
..
Suggested buffer size (FC on): 512K
Suggested buffer size (FC off, jumbo): 40Kb
7.1 Receive Functionality
Packet reception consists of:
• Recognizing the presence of a packet on the wire
• Performing address filtering
• DMA queue assignment
• Storing the packet in the receive data FIFO
----------------------------------- ^^^^^^^^^^^
• Transferring the data to assigned receive queues in host memory
• Updating the state of a receive descriptor.
7.1.9.1 Low Receive Descriptors Threshold
The number of usable (free) descriptors for the hardware is the distance
between the Tail
and Head registers. When the tail reaches the head, there are no free
descriptors and
further packets might be either dropped or block the receive FIFO. In
order to avoid this
situation, the 82599 might generate a low latency interrupt (associated
to the relevant
similar but always suspected user errors.
The fact that a starved queue can consume the entire internal
buffer seems a really bad bug.
At least you can overcome this one by having the demux done
in software.
Well, yes. Despite the fact that 82599 can handle huge (65k) RX queues,
this does not help much
unless there is some knob to prevent HOL.
cheers
luigi
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