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Date:   Tue, 10 Oct 2023 11:46:08 +0800
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Subject: Re: [PATCH net-next v7] net/core: Introduce netdev_core_stats_inc()
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To:     Steven Rostedt <rostedt@goodmis.org>
Cc:     Eric Dumazet <edumazet@google.com>, mhiramat@kernel.org,
        dennis@kernel.org, tj@kernel.org, cl@linux.com,
        mark.rutland@arm.com, davem@davemloft.net, kuba@kernel.org,
        pabeni@redhat.com, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org,
        Alexander Lobakin <aleksander.lobakin@intel.com>,
        linux-trace-kernel@vger.kernel.org, linux-mm@kvack.org
References: <20231007050621.1706331-1-yajun.deng@linux.dev>
 <CANn89i+navyRe8-AV=ehM3qFce2hmnOEKBqvK5Xnev7KTaS5Lg@mail.gmail.com>
 <a53a3ff6-8c66-07c4-0163-e582d88843dd@linux.dev>
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 <9f4fb613-d63f-9b86-fe92-11bf4dfb7275@linux.dev>
 <CANn89iK7bvQtGD=p+fHaWiiaNn=u8vWrt0YQ26pGQY=kZTdfJw@mail.gmail.com>
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 <296ca17d-cff0-2d19-f620-eedab004ddde@linux.dev>
 <CANn89iL=W3fyuH_KawfhKvLyw2Cw=qhHbEZtbKgQEYhHJChy3Q@mail.gmail.com>
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 <078f662d-a73f-766b-3a07-c82cd37026c5@linux.dev>
 <20231009102833.1b0d35e3@gandalf.local.home>
From:   Yajun Deng <yajun.deng@linux.dev>
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On 2023/10/9 22:28, Steven Rostedt wrote:
> On Mon, 9 Oct 2023 18:58:27 +0800
> Yajun Deng <yajun.deng@linux.dev> wrote:
>
>>> C compiler decides to inline or not, depending on various factors.
>>>
>>> The most efficient (and small) code is generated by this_cpu_inc()
>>> version, allowing the compiler to inline it.
>>>
>>> If you copy/paste this_cpu_inc()  twenty times, then the compiler
>>> would  not inline the function anymore.
> Yes, if you want something to be visible by ftrace, it must not be inlined
> (as inlined functions are not function calls by definition). And as Eric
> stated, the compiler is perfectly allowed to inline something if it
> believes it will be more efficient. i.e. There may be code around the function
> call that could be more efficient if it wasn't change to parameters. If you
> want to make sure a function stays out of line, you must explicitly tell
> the compiler you want the function not to ever be inlined (hence the
> "noinline" attribute).


Thanks for the details.

>>
>> Got it. Thank you.
> Great.
>
> -- Steve