Re: [bpf-next V2 PATCH 10/15] xdp: rhashtable with allocator ID to pointer mapping

[Jason Wang <jasowang@redhat.com>]

On 2018年03月09日 17:37, Jesper Dangaard Brouer wrote:
> On Fri, 9 Mar 2018 16:08:58 +0800
> Jason Wang<jasowang@redhat.com>  wrote:
>
>> On 2018年03月08日 21:08, Jesper Dangaard Brouer wrote:
>>> Use the IDA infrastructure for getting a cyclic increasing ID number,
>>> that is used for keeping track of each registered allocator per
>>> RX-queue xdp_rxq_info.  Instead of using the IDR infrastructure, which
>>> uses a radix tree, use a dynamic rhashtable, for creating ID to
>>> pointer lookup table, because this is faster.
>>>
>>> The problem that is being solved here is that, the xdp_rxq_info
>>> pointer (stored in xdp_buff) cannot be used directly, as the
>>> guaranteed lifetime is too short.  The info is needed on a
>>> (potentially) remote CPU during DMA-TX completion time . In an
>>> xdp_frame the xdp_mem_info is stored, when it got converted from an
>>> xdp_buff, which is sufficient for the simple page refcnt based recycle
>>> schemes.
>>>
>>> For more advanced allocators there is a need to store a pointer to the
>>> registered allocator.  Thus, there is a need to guard the lifetime or
>>> validity of the allocator pointer, which is done through this
>>> rhashtable ID map to pointer. The removal and validity of of the
>>> allocator and helper struct xdp_mem_allocator is guarded by RCU.  The
>>> allocator will be created by the driver, and registered with
>>> xdp_rxq_info_reg_mem_model().
>>>
>>> It is up-to debate who is responsible for freeing the allocator
>>> pointer or invoking the allocator destructor function.  In any case,
>>> this must happen via RCU freeing.
>>>
>>> Use the IDA infrastructure for getting a cyclic increasing ID number,
>>> that is used for keeping track of each registered allocator per
>>> RX-queue xdp_rxq_info.
>>>
>>> Signed-off-by: Jesper Dangaard Brouer<brouer@redhat.com>   
>> A stupid question is, can we manage to unify this ID with NAPI id?
> Sorry I don't understand the question?

I mean can we associate page poll pointer to napi_struct, record NAPI id 
in xdp_mem_info and do lookup through NAPI id?

Thanks