Re: [dpdk-dev] [EXT] Re: [PATCH v6 0/4] add IOVA = VA support in KNI

[Vamsi Krishna Attunuru <vattunuru@marvell.com>]

> -----Original Message-----
> From: Olivier Matz <olivier.matz@6wind.com>
> Sent: Tuesday, July 16, 2019 3:26 PM
> To: Vamsi Krishna Attunuru <vattunuru@marvell.com>
> Cc: Burakov, Anatoly <anatoly.burakov@intel.com>; Jerin Jacob Kollanukkaran
> <jerinj@marvell.com>; Ferruh Yigit <ferruh.yigit@intel.com>; dev@dpdk.org;
> arybchenko@solarflare.com
> Subject: Re: [dpdk-dev] [EXT] Re: [PATCH v6 0/4] add IOVA = VA support in KNI
> 
> Hi,
> 
> On Tue, Jul 16, 2019 at 09:40:59AM +0000, Vamsi Krishna Attunuru wrote:
> >
> >
> > > -----Original Message-----
> > > From: Olivier Matz <olivier.matz@6wind.com>
> > > Sent: Tuesday, July 16, 2019 2:17 PM
> > > To: Burakov, Anatoly <anatoly.burakov@intel.com>
> > > Cc: Jerin Jacob Kollanukkaran <jerinj@marvell.com>; Ferruh Yigit
> > > <ferruh.yigit@intel.com>; Vamsi Krishna Attunuru
> > > <vattunuru@marvell.com>; dev@dpdk.org; arybchenko@solarflare.com
> > > Subject: Re: [dpdk-dev] [EXT] Re: [PATCH v6 0/4] add IOVA = VA
> > > support in KNI
> > >
> > > Hi,
> > >
> > > On Mon, Jul 15, 2019 at 10:38:53AM +0100, Burakov, Anatoly wrote:
> > > > On 15-Jul-19 5:54 AM, Jerin Jacob Kollanukkaran wrote:
> > > > > > > > > > > (also, i don't really like the name NO_PAGE_BOUND
> > > > > > > > > > > since in memzone API there's a "bounded memzone"
> > > > > > > > > > > allocation API, and this flag's name reads like
> > > > > > > > > > > objects would not be bounded by page size, not that
> > > > > > > > > > > they won't cross page
> > > > > > > > > > > boundary)
> > > > > > > > > >
> > > > > > > > > > No strong opinion for the name. What name you suggest?
> > > > > > > > >
> > > > > > > > > How about something like MEMPOOL_F_NO_PAGE_SPLIT?
> > > > > > > >
> > > > > > > > Looks good to me.
> > > > > > > >
> > > > > > > > In summary, Change wrt existing patch"
> > > > > > > > - Change NO_PAGE_BOUND to MEMPOOL_F_NO_PAGE_SPLIT
> > > > > > > > - Set this flag in  rte_pktmbuf_pool_create () when
> > > > > > > rte_eal_has_hugepages() ||
> > > > > > > >    rte_malloc_heap_socket_is_external(socket_id))
> > > > > > >
> > > > > > > If we are to have a special KNI allocation API, would we even need
> that?
> > > > > >
> > > > > > Not need this change in rte_pktmbuf_pool_create () if we
> > > > > > introduce a new rte_kni_pktmbuf_pool_create () API.
> > > > >
> > > > > Ferruh, Olivier, Anatoly,
> > > > >
> > > > > Any objection to create new rte_kni_pktmbuf_pool_create () API
> > > > > to embedded MEMPOOL_F_NO_PAGE_SPLIT flag requirement for KNI +
> > > > > IOVA
> > > as
> > > > > VA
> > > > >
> > > > >
> > > >
> > > > As long as we all are aware of what that means and agree with that
> > > > consequence (namely, separate codepaths for KNI and other PMD's)
> > > > then i have no specific objections.
> > >
> > > Sorry for the late feedback.
> > >
> > > I think we can change the default behavior of mempool populate(), to
> > > prevent objects from being accross 2 pages, except if the size of
> > > the object is bigger than the size of the page. This is already what
> > > is done in
> > > rte_mempool_op_calc_mem_size_default() when we want to estimate the
> > > amount of memory needed to allocate N objects.
> > >
> > > This would avoid the introduction of a specific API to allocate
> > > packets for kni, and a specific mempool flag.
> > >
> > > About the problem of 9K mbuf mentionned by Anatoly, could we imagine
> > > a check in kni code, that just returns an error "does not work with
> > > size(mbuf) > size(page)" ?
> > >
> >
> > Yes, change in default behavior avoids new APIs or flags.
> > Two minor changes on top of  above suggestions.
> > 1) Can flag(NO_PAGE_SPLIT) be retained.?,  sequence is like,  flag is
> > set by default in rte_mempool_populate_default() and later it can be
> > cleared based on obj_per_page in rte_mempool_op_calc_mem_size_default().
> I do not see specific requirement of these flag apart from handling above
> sequence.
> 
> Sorry, I don't get why you want to keep this flag. Is it to facilitate the error check
> in kni code?
Yes, it's only for error check I thought.

> 
> The flags are used by the mempool user to ask for a specific behavior, so if we
> change the default behavior, there is nothing to change to the user API.

Correct, the flags are meant for mempool users. As you suggested there is no requirement
of new APIs or flags by changing default behavior.

> 
> > 2) For problems of 9k mbuf, I think that check could be addressed in kni lib(in
> rte_kni_init and return error).
> 
> You can use rte_mempool_obj_iter() to iterate the objects (mbufs) in the
> mempool, to ensure that none of them is accross 2 pages.