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

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Date:   Fri, 9 Mar 2018 10:37:25 +0100
From:   Jesper Dangaard Brouer <brouer@...hat.com>
To:     Jason Wang <jasowang@...hat.com>
Cc:     netdev@...r.kernel.org,
        BjörnTöpel <bjorn.topel@...el.com>,
        magnus.karlsson@...el.com, 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>, brouer@...hat.com
Subject: Re: [bpf-next V2 PATCH 10/15] xdp: rhashtable with allocator ID to
 pointer mapping

On Fri, 9 Mar 2018 16:08:58 +0800
Jason Wang <jasowang@...hat.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@...hat.com>  
> 
> A stupid question is, can we manage to unify this ID with NAPI id?

Sorry I don't understand the question?

-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Principal Kernel Engineer at Red Hat
  LinkedIn: http://www.linkedin.com/in/brouer