Re: [PATCH v3 07/29] x86: bpf_jit, use ENTRY+ENDPROC

From: Jiri Slaby <jslaby@suse.cz>
To: David Miller <davem@davemloft.net>
Cc: alexei.starovoitov@gmail.com, mingo@redhat.com,
	tglx@linutronix.de, hpa@zytor.com, x86@kernel.org,
	jpoimboe@redhat.com, linux-kernel@vger.kernel.org,
	netdev@vger.kernel.org, daniel@iogearbox.net,
	edumazet@google.com
Subject: Re: [PATCH v3 07/29] x86: bpf_jit, use ENTRY+ENDPROC
Date: Mon, 24 Apr 2017 16:52:43 +0200	[thread overview]
Message-ID: <f7a94f4e-6d93-a447-a62f-3f290e66c647@suse.cz> (raw)
In-Reply-To: <20170424.104132.950580313142367896.davem@davemloft.net>

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