netdev - Re: [PATCH bpf-next 00/10] bpf: support offload of bpf_event

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Date:   Fri, 4 May 2018 23:46:12 +0200
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Jakub Kicinski <jakub.kicinski@...ronome.com>,
        alexei.starovoitov@...il.com
Cc:     oss-drivers@...ronome.com, netdev@...r.kernel.org
Subject: Re: [PATCH bpf-next 00/10] bpf: support offload of bpf_event_output()

On 05/04/2018 03:37 AM, Jakub Kicinski wrote:
> Hi!
> 
> This series centres on NFP offload of bpf_event_output().  The
> first patch allows perf event arrays to be used by offloaded
> programs.  Next patch makes the nfp driver keep track of such
> arrays to be able to filter FW events referring to maps.
> Perf event arrays are not device bound.  Having driver
> reimplement and manage the perf array seems brittle and unnecessary.
> 
> Patch 4 moves slightly the verifier step which replaces map fds
> with map pointers.  This is useful for nfp JIT since we can then
> easily replace host pointers with NFP table ids (patch 6).  This
> allows us to lift the limitation on map helpers having to be used
> with the same map pointer on all paths.  Second use of replacing
> fds with real host map pointers is that we can use the host map
> pointer as a key for FW events in perf event array offload.
> 
> Patch 5 adds perf event output offload support for the NFP.
> 
> There are some differences between bpf_event_output() offloaded
> and non-offloaded version.  The FW messages which carry events
> may get dropped and reordered relatively easily.  The return codes
> from the helper are also not guaranteed to match the host.  Users
> are warned about some of those discrepancies with a one time
> warning message to kernel logs.
> 
> bpftool gains an ability to dump perf ring events in a very simple
> format.  This was very useful for testing and simple debug, maybe
> it will be useful to others?
> 
> Last patch is a trivial comment fix.

Nice approach, applied to bpf-next, thanks Jakub!