Re: [dpdk-dev] time taken for allocation of mempool.

[Venumadhav Josyula <vjosyula@gmail.com>]

Hi Anatoly,

By default w/o specifying --iova-mode option is iova-mode=pa by default ?

Thanks
Venu

On Wed, 13 Nov, 2019, 10:56 pm Burakov, Anatoly, <anatoly.burakov@intel.com>
wrote:

> On 13-Nov-19 9:19 AM, Bruce Richardson wrote:
> > On Wed, Nov 13, 2019 at 10:37:57AM +0530, Venumadhav Josyula wrote:
> >> Hi ,
> >> We are using 'rte_mempool_create' for allocation of flow memory. This
> has
> >> been there for a while. We just migrated to dpdk-18.11 from dpdk-17.05.
> Now
> >> here is problem statement
> >>
> >> Problem statement :
> >> In new dpdk ( 18.11 ), the 'rte_mempool_create' take approximately ~4.4
> sec
> >> for allocation compared to older dpdk (17.05). We have som 8-9 mempools
> for
> >> our entire product. We do upfront allocation for all of them ( i.e. when
> >> dpdk application is coming up). Our application is run to completion
> model.
> >>
> >> Questions:-
> >> i)  is that acceptable / has anybody seen such a thing ?
> >> ii) What has changed between two dpdk versions ( 18.11 v/s 17.05 ) from
> >> memory perspective ?
> >>
> >> Any pointer are welcome.
> >>
> > Hi,
> >
> > from 17.05 to 18.11 there was a change in default memory model for DPDK.
> In
> > 17.05 all DPDK memory was allocated statically upfront and that used for
> > the memory pools. With 18.11, no large blocks of memory are allocated at
> > init time, instead the memory is requested from the kernel as it is
> needed
> > by the app. This will make the initial startup of an app faster, but the
> > allocation of new objects like mempools slower, and it could be this you
> > are seeing.
> >
> > Some things to try:
> > 1. Use "--socket-mem" EAL flag to do an upfront allocation of memory for
> use
> > by your memory pools and see if it improves things.
> > 2. Try using "--legacy-mem" flag to revert to the old memory model.
> >
> > Regards,
> > /Bruce
> >
>
> I would also add to this the fact that the mempool will, by default,
> attempt to allocate IOVA-contiguous memory, with a fallback to non-IOVA
> contiguous memory whenever getting IOVA-contiguous memory isn't possible.
>
> If you are running in IOVA as PA mode (such as would be the case if you
> are using igb_uio kernel driver), then, since it is now impossible to
> preallocate large PA-contiguous chunks in advance, what will likely
> happen in this case is, mempool will try to allocate IOVA-contiguous
> memory, fail and retry with non-IOVA contiguous memory (essentially
> allocating memory twice). For large mempools (or large number of
> mempools) that can take a bit of time.
>
> The obvious workaround is using VFIO and IOVA as VA mode. This will
> cause the allocator to be able to get IOVA-contiguous memory at the
> outset, and allocation will complete faster.
>
> The other two alternatives, already suggested in this thread by Bruce
> and Olivier, are:
>
> 1) use bigger page sizes (such as 1G)
> 2) use legacy mode (and lose out on all of the benefits provided by the
> new memory model)
>
> The recommended solution is to use VFIO/IOMMU, and IOVA as VA mode.
>
> --
> Thanks,
> Anatoly
>