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From: "Toke Høiland-Jørgensen" <toke@redhat.com>
To: "Björn Töpel" <bjorn.topel@gmail.com>,
	netdev@vger.kernel.org, ast@kernel.org, daniel@iogearbox.net
Cc: "Björn Töpel" <bjorn.topel@intel.com>,
	bpf@vger.kernel.org, magnus.karlsson@gmail.com,
	magnus.karlsson@intel.com, sridhar.samudrala@intel.com
Subject: Re: [PATCH bpf-next] libbpf: remove explicit XSKMAP lookup from AF_XDP XDP program
Date: Sun, 20 Oct 2019 21:53:19 +0200	[thread overview]
Message-ID: <87pnirb3dc.fsf@toke.dk> (raw)
In-Reply-To: <20191020170711.22082-1-bjorn.topel@gmail.com>

Björn Töpel <bjorn.topel@gmail.com> writes:

> From: Björn Töpel <bjorn.topel@intel.com>
>
> In commit 43e74c0267a3 ("bpf_xdp_redirect_map: Perform map lookup in
> eBPF helper") the bpf_redirect_map() helper learned to do map lookup,
> which means that the explicit lookup in the XDP program for AF_XDP is
> not needed.
>
> This commit removes the map lookup, which simplifies the BPF code and
> improves the performance for the "rx_drop" [1] scenario with ~4%.

Nice, 4% is pretty good!

I wonder if the program needs to be backwards-compatible (with pre-5.3
kernels), though?

You can do that by something like this:

ret = bpf_redirect_map(&xsks_map, index, XDP_PASS);
if (ret > 0)
  return ret;

if (bpf_map_lookup_elem(&xsks_map, &index))
   return bpf_redirect_map(&xsks_map, index, 0);
return XDP_PASS;


This works because bpf_redirect_map() prior to 43e74c0267a3 will return
XDP_ABORTED on a non-0 flags value.

-Toke


  reply	other threads:[~2019-10-20 19:53 UTC|newest]

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-10-20 17:07 Björn Töpel
2019-10-20 19:53 ` Toke Høiland-Jørgensen [this message]
2019-10-21  5:03   ` Björn Töpel

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