Re: [PATCH net-next v10 05/14] netdev: netdevice devmem allocator

Steven Rostedt
2024-06-06T01:43:35Z

On Wed, 5 Jun 2024 02:52:29 +0200
Andrew Lunn <andrew@lunn.ch> wrote:

> > How is a compiler going to know that?
>
> It might have some heuristics to try to guess unlikely/likely, but
> that is not what we are talking about here.
>
> How much difference did 'always_inline' and 'noinline' make? Hopefully
> the likely is enough of a clue it should prefer to inline whatever is
> in that branch, where as for the unlikely case it can do a function
> call.

Perhaps, but one of the issues was that I have lots of small functions that
are used all over the place, and gcc tends to change them to function
calls, instead of duplicating them. I did this analysis back in 2016, so
maybe it became better.

>
> But compilers is not my thing, which is why i would reach out to the
> compiler people and ask them, is it expected to get this wrong, could
> it be made better?

Well, I actually do work with the compiler folks, and we are actually
trying to get a session at GNU Cauldron where Linux kernel folks can talk
with the gcc compiler folks.

I've stared at so many objdump outputs, that I can now pretty much see the
assembly that my C code makes ;-)

-- Steve