Re: [dpdk-dev] [PATCH] mempool: allow for user-owned mempool caches

["Mauricio Vásquez" <mauricio.vasquezbernal@studenti.polito.it>]

Hello to everybody,

I find this proposal very interesting as It could be used to solve an issue
that has not been mentioned yet: using memory pools shared with ivshmem.
Currently, due to the per lcore cache, it is not possible to allocate and
deallocate packets from the guest as it will cause cache corruption because
DPDK processes in the guest and in the host share some lcores_id.

If there is an API to register caches, the EAL could create and register
its own caches during the ivshmem initialization in the guest, avoiding
possible cache corruption problems.

I look forward to V2 in order to get a clear idea of how can it be used to
solve this issue.

Mauricio V,

On Fri, Mar 25, 2016 at 11:55 AM, Olivier Matz <olivier.matz@6wind.com>
wrote:

> Hi Venky,
>
> >> The main benefit of having an external cache is to allow mempool users
> >> (threads) to maintain a local cache even though they don't have a valid
> >> lcore_id (non-EAL threads). The fact that cache access is done by
> indexing
> >> with the lcore_id is what makes it difficult...
> >
> > Hi Lazaros,
> >
> > Alternative suggestion: This could actually be very simply done via
> creating an EAL API to register and return an lcore_id for a thread wanting
> to use DPDK services. That way, you could simply create your pthread, call
> the eal_register_thread() function that assigns an lcore_id to the caller
> (and internally sets up the per_lcore variable.
> >
> > The advantage of doing it this way is that you could extend it to other
> things other than the mempool that may need an lcore_id setup.
>
> From my opinion, externalize the cache structure as Lazaros suggests
> would make things simpler, especially in case of dynamic threads
> allocation/destruction.
>
> If a lcore_id regristration API is added in EAL, we still need a
> max lcore value when the mempool is created so the cache can be
> allocated. Moreover, the API would not be as simple, especially
> if it needs to support secondary processes.
>
>
> Regards,
> Olivier
>