netdev - Re: [PATCH net-next 00/13] nfp: bpf: jump resolution and memcpy update

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Date:   Fri, 1 Dec 2017 21:04:40 +0100
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Jakub Kicinski <jakub.kicinski@...ronome.com>,
        netdev@...r.kernel.org
Cc:     oss-drivers@...ronome.com
Subject: Re: [PATCH net-next 00/13] nfp: bpf: jump resolution and memcpy
 update

On 12/01/2017 06:32 AM, Jakub Kicinski wrote:
> Hi!
> 
> Jiong says:
> 
> Currently, compiler will lower memcpy function call in XDP/eBPF C program
> into a sequence of eBPF load/store pairs for some scenarios.
> 
> Compiler is thinking this "inline" optimiation is beneficial as it could
> avoid function call and also increase code locality.
> 
> However, Netronome NPU is not an tranditional load/store architecture that
> doing a sequence of individual load/store actions are not efficient.
> 
> This patch set tries to identify the load/store sequences composed of
> load/store pairs that comes from memcpy lowering, then accelerates them
> through NPU's Command Push Pull (CPP) instruction.
> 
> This patch set registered an new optimization pass before doing the actual
> JIT work, it traverse through eBPF IR, once found candidate sequence then
> record the memory copy source, destination and length information in the
> first load instruction starting the sequence and marks all remaining
> instructions in the sequence into skipable status. Later, when JITing the
> first load instructoin, optimal instructions will be generated using those
> record information.
> 
> For this safety of this transformation:
> 
>   - jump into the middle of the sequence will cancel the optimization.
> 
>   - overlapped memory access will cancel the optimization.
> 
>   - the load destination register still contains the same value as before
>     the transformation.

Series applied to bpf-next, thanks guys!