Hi Nelio,
Let me provide more background.
The context is TRex running in Advance Stateful (ASTf) mode using multi-core.
In this case the flows are distributed using RSS. New flows (c->s) need to have
a tuple that will match the generated core. For this calculation there is a
need of to know the *RETA table size*
Code:
/*1. verify that driver can support RSS */
rte_eth_dev_info_get(m_repid,&dev_info);
save_reta_size = dev_info.reta_size
save_hash_key = dev_info.hash_key_size
printf("RETA_SIZE : %d \n",save_reta_size);
printf("HASH_SIZE : %d \n",save_hash_key);
/*2. configure queues */
ret = rte_eth_dev_configure(m_repid,
nb_rx_queue,
nb_tx_queue,
eth_conf);
..
/* 3. reading the RETA again */
rte_eth_dev_info_get(m_repid,&dev_info);
save_reta_size = dev_info.reta_size <<
save_hash_key = dev_info.hash_key_size
printf("RETA_SIZE1 : %d \n",save_reta_size);
/* 4. update the RETA table */
rte_eth_dev_rss_reta_update(m_repid, &reta_conf[0], dev_info.reta_size)
2. /*Output in case of Intel i40e*/
RETA_SIZE : 512
HASH_SIZE : 52
RETA_SIZE1 : 512
3. /*Output in case of Mlx5 */
RETA_SIZE : 512
HASH_SIZE : 0
RETA_SIZE1 : 4 << not round of 64 , depends on the number of rx queues
Hanoh
-----Original Message-----
From: Nélio Laranjeiro [mailto:nelio.laranje...@6wind.com]
Sent: Thursday, March 22, 2018 11:28 AM
To: Hanoch Haim (hhaim)
Cc: Yongseok Koh; dev@dpdk.org
Subject: Re: [dpdk-dev] mlx5 reta size is dynamic
Hi Hanoch,
On Thu, Mar 22, 2018 at 09:02:19AM +0000, Hanoch Haim (hhaim) wrote:
> Hi Nelio,
> I think you didn't understand me. I suggest to keep the RETA table
> size constant (maximum 512 in your case) and don't change its base on
> the number of configured Rx-queue.
It is even simpler, we can return the maximum size or a multiple of
RTE_RETA_GROUP_SIZE according to the number of Rx queues being used, in the
devop->dev_infos_get() as it is what the
rte_eth_dev_rss_reta_update() implementation will expect.
> This will make the DPDK API consistent. As a user I need to do tricks
> (allocate an odd/prime number of rx-queues) to get the RETA size
> constant at 512
I understand this issue, what I don't fully understand your needs.
> I'm not talking about changing the values in the RETA table which can
> be done while there is traffic.
On MLX5 changing the entries of the RETA table don't affect the current
traffic, it needs a port restart to affect it and only for "default"
flows, any flow created through the public flow API are not impacted by the
RETA table.
>From my understanding, you wish to have a size returned by
devop->dev_infos_get() usable directly by rte_eth_dev_rss_reta_update().
This is why you are asking for a fix size? So, if internally the PMD starts
with a smaller RETA table does not really matter, until the RETA API works
without any trick from the application side. Is this correct?
Thanks,
> Thanks,
> Hanoh
>
>
> -----Original Message-----
> From: Nélio Laranjeiro [mailto:nelio.laranje...@6wind.com]
> Sent: Thursday, March 22, 2018 10:55 AM
> To: Hanoch Haim (hhaim)
> Cc: Yongseok Koh; dev@dpdk.org
> Subject: Re: [dpdk-dev] mlx5 reta size is dynamic
>
> On Thu, Mar 22, 2018 at 06:52:53AM +0000, Hanoch Haim (hhaim) wrote:
> > Hi Yongseok,
> >
> >
> > RSS has a DPDK API,application can ask for the reta table size and
> > configure it. In your case you are assuming specific use case and
> > change the size dynamically which solve 90% of the use-cases but
> > break the 10% use-case.
> > Instead, you could provide the application a consistent API and with
> > that 100% of the applications can work with no issue. This is what
> > happen with Intel (ixgbe/i40e) Another minor issue the rss_key_size
> > return as zero but internally it is 40 bytes
>
> Hi Hanoch,
>
> Legacy DPDK API has always considered there is only a single indirection
> table aka. RETA whereas this is not true [1][2] on this device.
>
> On MLX5 there is an indirection table per Hash Rx queue according to the list
> of queues making part of it.
> The Hash Rx queue is configured to make the hash with configured
> information:
> - Algorithm,
> - key
> - hash field (Verbs hash field)
> - Indirection table
> An Hash Rx queue cannot handle multiple RSS configuration, we have an Hash Rx
> queue per protocol and thus a full configuration per protocol.
>
> In such situation, changing the RETA means stopping the traffic, destroying
> every single flow, hash Rx queue, indirection table to remake everything with
> the new configuration.
> Until then, we always recommended to any application to restart the port on
> this device after a RETA update to apply this new configuration.
>
> Since the flow API is the new way to configure flows, application should move
> to this new one instead of using old API for such behavior.
> We should also remove such devop from the PMD to avoid any confusion.
>
> Regards,
>
> > Thanks,
> > Hanoh
> >
> > -----Original Message-----
> > From: Yongseok Koh [mailto:ys...@mellanox.com]
> > Sent: Wednesday, March 21, 2018 11:48 PM
> > To: Hanoch Haim (hhaim)
> > Cc: dev@dpdk.org
> > Subject: Re: [dpdk-dev] mlx5 reta size is dynamic
> >
> > On Wed, Mar 21, 2018 at 06:56:33PM +0000, Hanoch Haim (hhaim) wrote:
> > > Hi mlx5 driver expert,
> > >
> > > DPDK: 17.11
> > > Any reason mlx5 driver change the rate table size dynamically
> > > based on the rx- queues# ?
> >
> > The device only supports 2^n-sized indirection table. For example, if the
> > number of Rx queues is 6, device can't have 1-1 mapping but the size of ind
> > tbl could be 8, 16, 32 and so on. If we configure it as 8 for example, 2
> > out of 6 queues will have 1/4 of traffic while the rest 4 queues receives
> > 1/8. We thought it was too much disparity and preferred setting the max
> > size in order to mitigate the imbalance.
> >
> > > There is a hidden assumption that the user wants to distribute the
> > > packets evenly which is not always correct.
> >
> > But it is mostly correct because RSS is used for uniform distribution. The
> > decision wasn't made based on our speculation but by many request from
> > multiple customers.
> >
> > > /* If the requested number of RX queues is not a power of two, use the
> > > * maximum indirection table size for better balancing.
> > > * The result is always rounded to the next power of two. */
> > > reta_idx_n = (1 << log2above((rxqs_n & (rxqs_n - 1)) ?
> > > priv->ind_table_max_size :
> > > rxqs_n));
> >
> > Thanks,
> > Yongseok
>
> [1] https://dpdk.org/ml/archives/dev/2015-October/024668.html
> [2] https://dpdk.org/ml/archives/dev/2015-October/024669.html
>
> --
> Nélio Laranjeiro
> 6WIND
--
Nélio Laranjeiro
6WIND
