Re: transmit functions of dpdk

On Wed, Dec 10, 2014 at 01:09:32PM +0100, Sachin Sharma wrote:

Hi Bruce,

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I'm not entirely clear on what you mean by filling one queue and

emptying another. Is this just a form of buffering you are trying to
implement?

Yes, you are right! I am implementing a buffering mechanism in which a node
will have three queues and it  fills one queue with packets and when the
queue is full then transmit the packets from the queue to the wire and
while filling one queue, it can transmit packets to a wire through another
queue that is already full.

Thanks & Regards,
Sachin.

The standard sample applications with DPDK use a simple buffering scheme, where
we buffer the packets until a full burst of 32 are ready for sending. Once we
have a full burst of packets - or a timeout occurs - we then send that burst
of packets using tx_burst function. Would such a scheme not work for you?

NOTE: the tx_burst function returns as soon as the packets are written to the
NIC's TX ring and the NIC's tail pointer is updated. It does not actually wait
until all the packets are transmitted onto the wire. This means that your core
does not need to see about trying to do other tasks during the actual packet
transmission time, so you don't need a buffer for new packets arriving at the
core while the NIC is physically transmitting data.

Regards,
/Bruce

On Wed, Dec 10, 2014 at 12:45 PM, Bruce Richardson <
bruce.richardson-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org> wrote:

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On Wed, Dec 10, 2014 at 12:31:27PM +0100, Sachin Sharma wrote:

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Hi Bruce,

In my use case, I want to have three NIC TX queues per port, and want to
fill one NIC TX queue and want to empty the other queue. Is it possible
this through tx_burst or do I need to implement these queues in
applications as you suggested before. However, in this case, I would have
then one NIC TX queues and three queues in an application which actually
transmits packets to this NIC TX queue. Am I right?

For the suggestion I made, yes, you would have three software queues in
your
application, and a single TX on the NIC - though you could also have a 1:1
mapping
of software to HW queues if you wanted.
However, I'm not entirely clear on what you mean by filling one queue and
emptying
another. Is this just a form of buffering you are trying to implement?

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Thanks,
Sachin.

On Wed, Dec 10, 2014 at 12:22 PM, Bruce Richardson <
bruce.richardson-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org> wrote:

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On Wed, Dec 10, 2014 at 12:03:41PM +0100, Sachin Sharma wrote:

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Dear all,

 In my algorithm, I am interested to perform  two activities - (1)
transmitting packets to a tx_queue and (2) transmitting packets from
tx_queue to a wire - separately. I have gone through the code by

putting

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logs in the dpdk code and found that there is a function

rte_eth_tx_burst

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which transmits packets to a specific queue. However, when I debugged

more

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then I found that this function just calls eth_igb_xmit_pkts
from librte_pmd_e1000, and this function just directly write the

packets

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to

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the wire by writing all packets into registers. Could you please

suggest

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how to implement these two functions if these are not implemented

already

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in dpdk?



Thanks & Regards,
Sachin.

Hi Sachin,

anything written to the NIC TX queue is automatically put onto the wire
unless
the NIC port is down or the wire is unplugged etc. What is your

use-case

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that you
need to do this? I would suggest doing internal buffering in your
application,
as many DPDK example applications do, and then call tx_burst to put

your

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packets
on the wire when you want this capability.

Regards,
/Bruce