netdev - Re: [PATCH bpf] bpf: powerpc64: optimize JIT passes for bpf function calls

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Message-ID: <0e55ce74-ea93-06cf-cc67-28708f978bc2@iogearbox.net>
Date:   Mon, 3 Dec 2018 13:48:10 +0100
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Sandipan Das <sandipan@...ux.ibm.com>, ast@...nel.org
Cc:     naveen.n.rao@...ux.ibm.com, mpe@...erman.id.au,
        linuxppc-dev@...ts.ozlabs.org, netdev@...r.kernel.org
Subject: Re: [PATCH bpf] bpf: powerpc64: optimize JIT passes for bpf function
 calls

Hi Sandipan,

On 12/03/2018 01:21 PM, Sandipan Das wrote:
> Once the JITed images for each function in a multi-function program
> are generated after the first three JIT passes, we only need to fix
> the target address for the branch instruction corresponding to each
> bpf-to-bpf function call.
> 
> This introduces the following optimizations for reducing the work
> done by the JIT compiler when handling multi-function programs:
> 
>   [1] Instead of doing two extra passes to fix the bpf function calls,
>       do just one as that would be sufficient.
> 
>   [2] During the extra pass, only overwrite the instruction sequences
>       for the bpf-to-bpf function calls as everything else would still
>       remain exactly the same. This also reduces the number of writes
>       to the JITed image.
> 
>   [3] Do not regenerate the prologue and the epilogue during the extra
>       pass as that would be redundant.
> 
> Signed-off-by: Sandipan Das <sandipan@...ux.ibm.com>

Thanks for the patch, just to clarify, it's targeted at bpf-next and
not bpf, correct?

Thanks,
Daniel