Re: [dpdk-dev] Aligned RX data.

["Ananyev, Konstantin" <konstantin.ananyev@intel.com>]

> -----Original Message-----
> From: Ananyev, Konstantin
> Sent: Monday, October 13, 2014 12:30 PM
> To: Ananyev, Konstantin
> Subject: FW: [dpdk-dev] Aligned RX data.
> 
> 
> 
> From: Alex Markuze [mailto:alex@weka.io]
> Sent: Monday, October 13, 2014 9:47 AM
> To: Ananyev, Konstantin
> Cc: dev@dpdk.org
> Subject: Re: [dpdk-dev] Aligned RX data.
> 
> Hi All,
> Is there a way to create a mempool such that all mbufs are aligned to X. lets say X is 512.
> 
> Thanks.
> 

For example something like that:

struct rte_mempool *
mempool_xz1_create(uint32_t elt_num, int32_t socket_id)
{
        struct rte_mempool *mp;
        const struct rte_memzone *mz;
        struct rte_mempool_objsz obj_sz;
        uint32_t flags, elt_size, total_size;
        size_t sz;
        phys_addr_t pa;
        void *va;

        /* mp element header_size==64B,  trailer_size==0. */
        flags = MEMPOOL_F_NO_SPREAD;

        /* to make total element size of mp 2K. */
        elt_size = 2048 - 64;

        total_size = rte_mempool_calc_obj_size(elt_size, flags, &obj_sz);
        sz = elt_num * total_size + 512;

        if ((mz = rte_memzone_reserve_aligned("xz1_obj", sz, socket_id,
                        0, 512)) == NULL)
                return (NULL);

        va = (char *)mz->addr + 512 - obj_sz.header_size;
        pa = mz->phys_addr + 512 - obj_sz.header_size;

        mp = rte_mempool_xmem_create("xz1", elt_num, elt_size,
                256, sizeof(struct rte_pktmbuf_pool_private),
                rte_pktmbuf_pool_init, NULL,
                rte_pktmbuf_init, NULL,
                socket_id, flags, va, &pa,
                MEMPOOL_PG_NUM_DEFAULT, MEMPOOL_PG_SHIFT_MAX);

        return (mp);
}

Each mbuf will be aligned on 512B boundary and  1856 (2K - 64B header - 128B mbuf).

Alternative way - is to provide your own element constructor instead of rte_pktmbuf_init() for mempool_create.
And inside it align buf_addr and buf_physaddr.
Though in that case you have to set RTE_MBUF_REFCNT=n in your config.
That's why I'd say it is a not recommended.

Konstantin

> 
> On Sat, Oct 11, 2014 at 5:04 PM, Alex Markuze <alex@weka.io> wrote:
> O.k, And how would I do that?
> I'm guessing there is something I can control in rte_pktmbuf_pool_init?
> I would appreciate If you could spare a word or two in the matter.
> 
> On Tue, Oct 7, 2014 at 7:11 PM, Ananyev, Konstantin <konstantin.ananyev@intel.com> wrote:
> 
> 
> > -----Original Message-----
> > From: Ananyev, Konstantin
> > Sent: Tuesday, October 07, 2014 5:03 PM
> > To: Ananyev, Konstantin
> > Subject: FW: [dpdk-dev] Aligned RX data.
> >
> >
> >
> > From: Alex Markuze [mailto:alex@weka.io]
> > Sent: Tuesday, October 07, 2014 4:52 PM
> > To: Ananyev, Konstantin
> > Cc: dev@dpdk.org
> > Subject: Re: [dpdk-dev] Aligned RX data.
> >
> > RTE_PKTMBUF_HEADROOM defines the headroom
> 
> Yes.
> 
> >this would be true only if the buff_start was aligned to 512 which is not.
> 
> As I said: " Make sure that your all your mbufs are aligned by 512".
> 
> Konstantin
> 
> >
> > On Tue, Oct 7, 2014 at 1:05 PM, Ananyev, Konstantin <konstantin.ananyev@intel.com> wrote:
> >
> >
> > > -----Original Message-----
> > > From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Alex Markuze
> > > Sent: Tuesday, October 07, 2014 10:40 AM
> > > To: dev@dpdk.org
> > > Subject: [dpdk-dev] Aligned RX data.
> > >
> > > Hi , I'm trying to receive aligned packets from the wire.
> > > Meaning that for all received packets the pkt.data is always aligned to
> > > (512 -H).
> > >
> > > Looking at the pmds of ixgbe/vmxnet I see that the pmds call
> > > __rte_mbuf_raw_alloc and set the rx descriptor with a
> > > RTE_MBUF_DATA_DMA_ADDR_DEFAULT
> > > Instead of the more appropriate RTE_MBUF_DATA_DMA_ADDR.
> > >
> > > Do I need to modify each pmd I'm using to be able to receive aligned data?
> > Make sure that your all your mbufs are aligned by 512 and set in your config RTE_PKTMBUF_HEADROOM=512-H?
> >
> >
> > > Or have I missed something?
> > >
> > > Thanks
>