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Subject: Re: [PATCH net-next] net: Drop unlikely before IS_ERR(_OR_NULL)
To:     Kefeng Wang <wangkefeng.wang@huawei.com>,
        Jesse Brandeburg <jesse.brandeburg@intel.com>
Cc:     linux-kernel@vger.kernel.org,
        "David S. Miller" <davem@davemloft.net>,
        Alexey Kuznetsov <kuznet@ms2.inr.ac.ru>,
        Hideaki YOSHIFUJI <yoshfuji@linux-ipv6.org>,
        Vlad Yasevich <vyasevich@gmail.com>,
        Neil Horman <nhorman@tuxdriver.com>,
        Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>,
        netdev@vger.kernel.org, linux-sctp@vger.kernel.org
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 <20190605091319.000054e9@intel.com>
 <721a48ce-c09a-a35e-86ae-eac5eec26668@huawei.com>
From:   "Enrico Weigelt, metux IT consult" <lkml@metux.net>
Organization: metux IT consult
Message-ID: <37cbb3d8-bec8-4dd7-ba1f-31a2919316ca@metux.net>
Date:   Thu, 6 Jun 2019 22:41:32 +0200
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On 06.06.19 03:39, Kefeng Wang wrote:

Hi folks,

> There is no different in assembly output (only check the x86/arm64), and
> the Enrico Weigelt have finished a cocci script to do this cleanup.

I haven't compared the assembly output, just logically deduced from the
macro. If I understand it correctly, the likely()/unlikely() macros
just add a hint to the compiler, which branch it should optimize harder.

No idea what the compiler's actually doing, but I believe its things
like optimized shortcut evaluation and avoiding jumps to likely
branches.

>> I'm not sure in the end that the change is worth it, so would like you
>> to prove it is, unless davem overrides me. :-)

Depends on what you count as worthy ;-)

This patch just makes a source a bit more compact / easier to read.
But shouldn't have any actual consequence on the generated binary.


--mtx

-- 
Enrico Weigelt, metux IT consult
Free software and Linux embedded engineering
info@metux.net -- +49-151-27565287