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

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Message-ID: <ca2b27dc-243b-5b2e-6b05-a273c9e39aec@redhat.com>
Date:   Fri, 9 Mar 2018 16:08:58 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Jesper Dangaard Brouer <brouer@...hat.com>, netdev@...r.kernel.org,
        BjörnTöpel <bjorn.topel@...el.com>,
        magnus.karlsson@...el.com
Cc:     eugenia@...lanox.com, John Fastabend <john.fastabend@...il.com>,
        Eran Ben Elisha <eranbe@...lanox.com>,
        Saeed Mahameed <saeedm@...lanox.com>, galp@...lanox.com,
        Daniel Borkmann <borkmann@...earbox.net>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>,
        Tariq Toukan <tariqt@...lanox.com>
Subject: Re: [bpf-next V2 PATCH 10/15] xdp: rhashtable with allocator ID to
 pointer mapping



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@...hat.com>

A stupid question is, can we manage to unify this ID with NAPI id?

Thanks