[dpdk-dev] [PATCH] kni:optimization of rte_kni_rx_burst

[Hemant at freescale.com]

Hi OIivier
	 Comments inline.
Regards,
Hemant

> -----Original Message-----
> From: dev [mailto:dev-bounces at dpdk.org] On Behalf Of Olivier Deme
> Sent: 25/Feb/2015 5:44 PM
> To: dev at dpdk.org
> Subject: Re: [dpdk-dev] [PATCH] kni:optimization of rte_kni_rx_burst
> 
> Thank you Hemant, I think there might be one issue left with the patch though.
> The alloc_q must initially be filled with mbufs before getting mbuf back on the
> tx_q.
> 
> So the patch should allow rte_kni_rx_burst to check if alloc_q is empty.
> If so, it should invoke kni_allocate_mbufs(kni, 0) (to fill the alloc_q with
> MAX_MBUF_BURST_NUM mbufs)
> 
> The patch for rte_kni_rx_burst would then look like:
> 
> @@ -575,7 +575,7 @@ rte_kni_rx_burst(struct rte_kni *kni, struct rte_mbuf
> **mbufs, unsigned num)
> 
>       /* If buffers removed, allocate mbufs and then put them into alloc_q */
>       if (ret)
> -        kni_allocate_mbufs(kni);
> +      kni_allocate_mbufs(kni, ret);
> +  else if (unlikely(kni->alloc_q->write == kni->alloc_q->read))
> +      kni_allocate_mbufs(kni, 0);
> 
[hemant]  This will introduce a run-time check.

I missed to include the other change in the patch. 
 I am doing it in kni_alloc i.e. initiate the alloc_q with default burst size. 
	kni_allocate_mbufs(ctx, 0);

In a way, we are now suggesting to reduce the size of alloc_q to only default burst size. 

Can we reach is situation, when the kernel is adding packets faster in tx_q than the application is able to dequeue?
 alloc_q  can be empty in this case and kernel will be striving. 

> 
> Olivier.
> 
> On 25/02/15 11:48, Hemant Agrawal wrote:
> > From: Hemant Agrawal <hemant at freescale.com>
> >
> > if any buffer is read from the tx_q, MAX_BURST buffers will be allocated and
> attempted to be added to to the alloc_q.
> > This seems terribly inefficient and it also looks like the alloc_q will quickly fill
> to its maximum capacity. If the system buffers are low in number, it will reach
> "out of memory" situation.
> >
> > This patch allocates the number of buffers as many dequeued from tx_q.
> >
> > Signed-off-by: Hemant Agrawal <hemant at freescale.com>
> > ---
> >   lib/librte_kni/rte_kni.c | 13 ++++++++-----
> >   1 file changed, 8 insertions(+), 5 deletions(-)
> >
> > diff --git a/lib/librte_kni/rte_kni.c b/lib/librte_kni/rte_kni.c index
> > 4e70fa0..4cf8e30 100644
> > --- a/lib/librte_kni/rte_kni.c
> > +++ b/lib/librte_kni/rte_kni.c
> > @@ -128,7 +128,7 @@ struct rte_kni_memzone_pool {
> >
> >
> >   static void kni_free_mbufs(struct rte_kni *kni); -static void
> > kni_allocate_mbufs(struct rte_kni *kni);
> > +static void kni_allocate_mbufs(struct rte_kni *kni, int num);
> >
> >   static volatile int kni_fd = -1;
> >   static struct rte_kni_memzone_pool kni_memzone_pool = { @@ -575,7
> > +575,7 @@ rte_kni_rx_burst(struct rte_kni *kni, struct rte_mbuf
> > **mbufs, unsigned num)
> >
> >   	/* If buffers removed, allocate mbufs and then put them into alloc_q
> */
> >   	if (ret)
> > -		kni_allocate_mbufs(kni);
> > +		kni_allocate_mbufs(kni, ret);
> >
> >   	return ret;
> >   }
> > @@ -594,7 +594,7 @@ kni_free_mbufs(struct rte_kni *kni)
> >   }
> >
> >   static void
> > -kni_allocate_mbufs(struct rte_kni *kni)
> > +kni_allocate_mbufs(struct rte_kni *kni, int num)
> >   {
> >   	int i, ret;
> >   	struct rte_mbuf *pkts[MAX_MBUF_BURST_NUM]; @@ -620,7 +620,10
> @@
> > kni_allocate_mbufs(struct rte_kni *kni)
> >   		return;
> >   	}
> >
> > -	for (i = 0; i < MAX_MBUF_BURST_NUM; i++) {
> > +	if (num == 0 || num > MAX_MBUF_BURST_NUM)
> > +		num = MAX_MBUF_BURST_NUM;
> > +
> > +	for (i = 0; i < num; i++) {
> >   		pkts[i] = rte_pktmbuf_alloc(kni->pktmbuf_pool);
> >   		if (unlikely(pkts[i] == NULL)) {
> >   			/* Out of memory */
> > @@ -636,7 +639,7 @@ kni_allocate_mbufs(struct rte_kni *kni)
> >   	ret = kni_fifo_put(kni->alloc_q, (void **)pkts, i);
> >
> >   	/* Check if any mbufs not put into alloc_q, and then free them */
> > -	if (ret >= 0 && ret < i && ret < MAX_MBUF_BURST_NUM)
> {MAX_MBUF_BURST_NUM
> >
> > +	if (ret >= 0 && ret < i && ret < num) {
> >   		int j;
> >
> >   		for (j = ret; j < i; j++)
> 
> --
> 	*Olivier Demé*
> *Druid Software Ltd.*
> *Tel: +353 1 202 1831*
> *Email: odeme at druidsoftware.com <mailto:odeme at druidsoftware.com>*
> *URL: http://www.druidsoftware.com*
> 	*Hall 7, stand 7F70.*
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