linux-kernel - Re: [PATCH v3 07/29] x86: bpf

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Date:   Mon, 24 Apr 2017 16:52:43 +0200
From:   Jiri Slaby <jslaby@...e.cz>
To:     David Miller <davem@...emloft.net>
Cc:     alexei.starovoitov@...il.com, mingo@...hat.com, tglx@...utronix.de,
        hpa@...or.com, x86@...nel.org, jpoimboe@...hat.com,
        linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
        daniel@...earbox.net, edumazet@...gle.com
Subject: Re: [PATCH v3 07/29] x86: bpf_jit, use ENTRY+ENDPROC

On 04/24/2017, 04:41 PM, David Miller wrote:
>> It cannot stay as-is simply because we want to know where the functions
>> end to inject debuginfo properly. The code above does not warrant for
>> any exception.
> 
> I totally and completely disagree.

You can disagree as you wish but there is really nothing special on the
bpf code with respect to annotations.

>> Executing a nop takes a little and having externally-callable functions
>> aligned can actually help performance (no, I haven't measured nor tested
>> the code). But sure, the tool is generic, so I can introduce a local
>> macros to avoid alignments in the functions:
> 
> Not for this case, it's a bunch of entry points all packed together
> intentionally so that SKB accesses of different access sizes (which is
> almost always the case) from BPF programs use the smallest amount of
> I-cache as possible.

And for that reason I suggested the special macros for the code (see the
macros in the e-mail you replied to again). So what problem do you
actually have with the suggested solution?

thanks,
-- 
js
suse labs