netdev - Re: [PATCH bpf-next 08/11] i40e: add AF

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Date:   Wed, 29 Aug 2018 21:14:28 +0200
From:   Jakub Kicinski <jakub.kicinski@...ronome.com>
To:     Björn Töpel <bjorn.topel@...il.com>
Cc:     magnus.karlsson@...el.com, magnus.karlsson@...il.com,
        alexander.h.duyck@...el.com, alexander.duyck@...il.com,
        ast@...nel.org, brouer@...hat.com, daniel@...earbox.net,
        netdev@...r.kernel.org, jesse.brandeburg@...el.com,
        anjali.singhai@...el.com, peter.waskiewicz.jr@...el.com,
        Björn Töpel <bjorn.topel@...el.com>,
        michael.lundkvist@...csson.com, willemdebruijn.kernel@...il.com,
        john.fastabend@...il.com, neerav.parikh@...el.com,
        mykyta.iziumtsev@...aro.org, francois.ozog@...aro.org,
        ilias.apalodimas@...aro.org, brian.brooks@...aro.org,
        u9012063@...il.com, pavel@...tnetmon.com, qi.z.zhang@...el.com
Subject: Re: [PATCH bpf-next 08/11] i40e: add AF_XDP zero-copy Rx support

On Tue, 28 Aug 2018 14:44:32 +0200, Björn Töpel wrote:
> From: Björn Töpel <bjorn.topel@...el.com>
> 
> This patch adds zero-copy Rx support for AF_XDP sockets. Instead of
> allocating buffers of type MEM_TYPE_PAGE_SHARED, the Rx frames are
> allocated as MEM_TYPE_ZERO_COPY when AF_XDP is enabled for a certain
> queue.
> 
> All AF_XDP specific functions are added to a new file, i40e_xsk.c.
> 
> Note that when AF_XDP zero-copy is enabled, the XDP action XDP_PASS
> will allocate a new buffer and copy the zero-copy frame prior passing
> it to the kernel stack.
> 
> Signed-off-by: Björn Töpel <bjorn.topel@...el.com>

Mm.. I'm surprised you don't run into buffer reuse issues that I had
when playing with AF_XDP.  What happens in i40e if someone downs the
interface?  Will UMEMs get destroyed?  Will the RX buffers get freed?

I'll shortly send an RFC with my quick and dirty RX buffer reuse queue,
FWIW.