Re: transmit functions of dpdk

From: Bruce Richardson <hidden>
Date: 2014-12-10 13:37:45

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

Hi Bruce,

quoted

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:

quoted

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

quoted

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?

quoted

Thanks,
Sachin.

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

quoted

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

quoted

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

quoted

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

rte_eth_tx_burst

quoted

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

more

quoted

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

packets

quoted

to

quoted

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

suggest

quoted

how to implement these two functions if these are not implemented

already

quoted

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

quoted

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

quoted

packets
on the wire when you want this capability.

Regards,
/Bruce

Re: transmit functions of dpdk

From: Sachin Sharma <hidden>
Date: 2014-12-10 14:14:13

Hi Bruce,

quoted

The standard sample applications with DPDK use a simple buffering

scheme, where

quoted

we buffer the packets until a full burst of 32 are ready for sending.

Once we

quoted

have a full burst of packets - or a timeout occurs - we then send that

burst

quoted

of packets using tx_burst function. Would such a scheme not work for you?

Perhaps, this scheme will give some timing issues to me. For me, time is
very critical issue.  In your example, NIC TX ring also does some kind of
buffering in uncontrolled manner (i.e., packets are transmitted to it
without knowing that it will buffer or will directly forward on wire).
However, in my case, I want to control the transmission onto wire and
buffering into NIC TX ring through my software. Therefore, I think that I
need to create three NIC TX ring per port rather than creating three
software queues and need to transmit on wire from those ring through my
software code. So, is there any way that I can control transmission of
packets through these NIC TX rings i.e, buffering and transmission on the
wire? or this is not possible?

Thanks & kind regards,
Sachin.


On Wed, Dec 10, 2014 at 2:37 PM, Bruce Richardson <
bruce.richardson-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org> wrote:

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

quoted

Hi Bruce,

quoted

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

quoted

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

quoted

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

quoted


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

quoted

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

quoted

Hi Bruce,

In my use case, I want to have three NIC TX queues per port, and

want to

quoted

fill one NIC TX queue and want to empty the other queue. Is it

possible

quoted

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

quoted

then one NIC TX queues and three queues in an application which

actually

quoted

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

quoted

mapping
of software to HW queues if you wanted.
However, I'm not entirely clear on what you mean by filling one queue

and

quoted

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

quoted

Thanks,
Sachin.

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

quoted

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

quoted

Dear all,

 In my algorithm, I am interested to perform  two activities -

(1)

quoted

transmitting packets to a tx_queue and (2) transmitting packets

from

quoted

tx_queue to a wire - separately. I have gone through the code by

putting

quoted

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

rte_eth_tx_burst

quoted

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

debugged

quoted

more

quoted

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

packets

quoted

to

quoted

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

suggest

quoted

how to implement these two functions if these are not implemented

already

quoted

in dpdk?



Thanks & Regards,
Sachin.

Hi Sachin,

anything written to the NIC TX queue is automatically put onto the

wire

quoted

unless
the NIC port is down or the wire is unplugged etc. What is your

use-case

quoted

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

quoted

packets
on the wire when you want this capability.

Regards,
/Bruce

`h`	back out one level
`j`	next message in thread
`k`	previous message in thread
`l`	drill in
`Esc`	close help / fold thread tree
`?`	toggle this help