[dpdk-dev] transmit functions of dpdk

[dpdk-dev] transmit functions of dpdk

[Sachin Sharma]

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
logs in the dpdk code and found that there is a function rte_eth_tx_burst
which transmits packets to a specific queue. However, when I debugged more
then I found that this function just calls eth_igb_xmit_pkts
from librte_pmd_e1000, and this function just directly write the packets to
the wire by writing all packets into registers. Could you please suggest
how to implement these two functions if these are not implemented already
in dpdk?



Thanks & Regards,
Sachin.

Re: [dpdk-dev] transmit functions of dpdk

[Bruce Richardson]

On Wed, Dec 10, 2014 at 12:03:41PM +0100, Sachin Sharma wrote:
> 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
> logs in the dpdk code and found that there is a function rte_eth_tx_burst
> which transmits packets to a specific queue. However, when I debugged more
> then I found that this function just calls eth_igb_xmit_pkts
> from librte_pmd_e1000, and this function just directly write the packets to
> the wire by writing all packets into registers. Could you please suggest
> how to implement these two functions if these are not implemented already
> 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 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 packets
on the wire when you want this capability.

Regards,
/Bruce

Re: [dpdk-dev] transmit functions of dpdk

[Sachin Sharma]

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?

Thanks,
Sachin.

On Wed, Dec 10, 2014 at 12:22 PM, Bruce Richardson <
bruce.richardson@intel.com> wrote:

> On Wed, Dec 10, 2014 at 12:03:41PM +0100, Sachin Sharma wrote:
> > 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
> > logs in the dpdk code and found that there is a function rte_eth_tx_burst
> > which transmits packets to a specific queue. However, when I debugged
> more
> > then I found that this function just calls eth_igb_xmit_pkts
> > from librte_pmd_e1000, and this function just directly write the packets
> to
> > the wire by writing all packets into registers. Could you please suggest
> > how to implement these two functions if these are not implemented already
> > 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
> 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
> packets
> on the wire when you want this capability.
>
> Regards,
> /Bruce
>

Re: [dpdk-dev] transmit functions of dpdk

[Bruce Richardson]

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

> Thanks,
> Sachin.
> 
> On Wed, Dec 10, 2014 at 12:22 PM, Bruce Richardson <
> bruce.richardson@intel.com> wrote:
> 
> > On Wed, Dec 10, 2014 at 12:03:41PM +0100, Sachin Sharma wrote:
> > > 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
> > > logs in the dpdk code and found that there is a function rte_eth_tx_burst
> > > which transmits packets to a specific queue. However, when I debugged
> > more
> > > then I found that this function just calls eth_igb_xmit_pkts
> > > from librte_pmd_e1000, and this function just directly write the packets
> > to
> > > the wire by writing all packets into registers. Could you please suggest
> > > how to implement these two functions if these are not implemented already
> > > 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
> > 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
> > packets
> > on the wire when you want this capability.
> >
> > Regards,
> > /Bruce
> >

Re: [dpdk-dev] transmit functions of dpdk

[Sachin Sharma]

Hi Bruce,

>>>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.




On Wed, Dec 10, 2014 at 12:45 PM, Bruce Richardson <
bruce.richardson@intel.com> wrote:

> On Wed, Dec 10, 2014 at 12:31:27PM +0100, Sachin Sharma wrote:
> > 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?
>
> > Thanks,
> > Sachin.
> >
> > On Wed, Dec 10, 2014 at 12:22 PM, Bruce Richardson <
> > bruce.richardson@intel.com> wrote:
> >
> > > On Wed, Dec 10, 2014 at 12:03:41PM +0100, Sachin Sharma wrote:
> > > > 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
> > > > logs in the dpdk code and found that there is a function
> rte_eth_tx_burst
> > > > which transmits packets to a specific queue. However, when I debugged
> > > more
> > > > then I found that this function just calls eth_igb_xmit_pkts
> > > > from librte_pmd_e1000, and this function just directly write the
> packets
> > > to
> > > > the wire by writing all packets into registers. Could you please
> suggest
> > > > how to implement these two functions if these are not implemented
> already
> > > > 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
> > > 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
> > > packets
> > > on the wire when you want this capability.
> > >
> > > Regards,
> > > /Bruce
> > >
>

Re: [dpdk-dev] transmit functions of dpdk

[Bruce Richardson]

On Wed, Dec 10, 2014 at 01:09:32PM +0100, Sachin Sharma wrote:
> Hi Bruce,
> 
> >>>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@intel.com> wrote:
> 
> > On Wed, Dec 10, 2014 at 12:31:27PM +0100, Sachin Sharma wrote:
> > > 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?
> >
> > > Thanks,
> > > Sachin.
> > >
> > > On Wed, Dec 10, 2014 at 12:22 PM, Bruce Richardson <
> > > bruce.richardson@intel.com> wrote:
> > >
> > > > On Wed, Dec 10, 2014 at 12:03:41PM +0100, Sachin Sharma wrote:
> > > > > 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
> > > > > logs in the dpdk code and found that there is a function
> > rte_eth_tx_burst
> > > > > which transmits packets to a specific queue. However, when I debugged
> > > > more
> > > > > then I found that this function just calls eth_igb_xmit_pkts
> > > > > from librte_pmd_e1000, and this function just directly write the
> > packets
> > > > to
> > > > > the wire by writing all packets into registers. Could you please
> > suggest
> > > > > how to implement these two functions if these are not implemented
> > already
> > > > > 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
> > > > 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
> > > > packets
> > > > on the wire when you want this capability.
> > > >
> > > > Regards,
> > > > /Bruce
> > > >
> >

Re: [dpdk-dev] transmit functions of dpdk

[Sachin Sharma]

Hi Bruce,
>>>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?

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@intel.com> wrote:

> On Wed, Dec 10, 2014 at 01:09:32PM +0100, Sachin Sharma wrote:
> > Hi Bruce,
> >
> > >>>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@intel.com> wrote:
> >
> > > On Wed, Dec 10, 2014 at 12:31:27PM +0100, Sachin Sharma wrote:
> > > > 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?
> > >
> > > > Thanks,
> > > > Sachin.
> > > >
> > > > On Wed, Dec 10, 2014 at 12:22 PM, Bruce Richardson <
> > > > bruce.richardson@intel.com> wrote:
> > > >
> > > > > On Wed, Dec 10, 2014 at 12:03:41PM +0100, Sachin Sharma wrote:
> > > > > > 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
> > > > > > logs in the dpdk code and found that there is a function
> > > rte_eth_tx_burst
> > > > > > which transmits packets to a specific queue. However, when I
> debugged
> > > > > more
> > > > > > then I found that this function just calls eth_igb_xmit_pkts
> > > > > > from librte_pmd_e1000, and this function just directly write the
> > > packets
> > > > > to
> > > > > > the wire by writing all packets into registers. Could you please
> > > suggest
> > > > > > how to implement these two functions if these are not implemented
> > > already
> > > > > > 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
> > > > > 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
> > > > > packets
> > > > > on the wire when you want this capability.
> > > > >
> > > > > Regards,
> > > > > /Bruce
> > > > >
> > >
>