netdev - RE: [Intel-wired-lan] [PATCH net] i40e: fix potential RX buffer starvation for AF

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Date:   Wed, 30 Jan 2019 19:41:58 +0000
From:   "Bowers, AndrewX" <andrewx.bowers@...el.com>
To:     "intel-wired-lan@...ts.osuosl.org" <intel-wired-lan@...ts.osuosl.org>
CC:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: RE: [Intel-wired-lan] [PATCH net] i40e: fix potential RX buffer
 starvation for AF_XDP

> -----Original Message-----
> From: Intel-wired-lan [mailto:intel-wired-lan-bounces@...osl.org] On
> Behalf Of Magnus Karlsson
> Sent: Tuesday, January 29, 2019 6:03 AM
> To: Karlsson, Magnus <magnus.karlsson@...el.com>; Topel, Bjorn
> <bjorn.topel@...el.com>; intel-wired-lan@...ts.osuosl.org
> Cc: netdev@...r.kernel.org
> Subject: [Intel-wired-lan] [PATCH net] i40e: fix potential RX buffer starvation
> for AF_XDP
> 
> When the RX rings are created they are also populated with buffers so that
> packets can be received. Usually these are kernel buffers, but for AF_XDP in
> zero-copy mode, these are user-space buffers and in this case the
> application might not have sent down any buffers to the driver at this point.
> And if no buffers are allocated at ring creation time, no packets can be
> received and no interupts will be generated so the napi poll function that
> allocates buffers to the rings will never get executed.
> 
> To rectify this, we kick the NAPI context of any queue with an attached
> AF_XDP zero-copy socket in two places in the code. Once after an XDP
> program has loaded and once after the umem is registered.
> This take care of both cases: XDP program gets loaded first then AF_XDP
> socket is created, and the reverse, AF_XDP socket is created first, then XDP
> program is loaded.
> 
> Fixes: 0a714186d3c0 ("i40e: add AF_XDP zero-copy Rx support")
> Signed-off-by: Magnus Karlsson <magnus.karlsson@...el.com>
> ---
>  drivers/net/ethernet/intel/i40e/i40e_main.c | 13 ++++++++++++-
> drivers/net/ethernet/intel/i40e/i40e_xsk.c  |  5 +++++
>  2 files changed, 17 insertions(+), 1 deletion(-)

Tested-by: Andrew Bowers <andrewx.bowers@...el.com>