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Date:   Tue, 22 Mar 2022 22:02:06 +0100
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Subject: Don't do arithmetic on anything smaller than 'int' (was: [PATCH v2]
 ice: use min_t() to make code cleaner in ice_gnss)
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To:     Jakub Kicinski <kuba@kernel.org>,
        David Laight <David.Laight@ACULAB.COM>
Cc:     Wan Jiabing <wanjiabing@vivo.com>,
        intel-wired-lan@lists.osuosl.org,
        LKML <linux-kernel@vger.kernel.org>, netdev@vger.kernel.org,
        Paolo Abeni <pabeni@redhat.com>,
        "David S. Miller" <davem@davemloft.net>
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From:   Paul Menzel <pmenzel@molgen.mpg.de>
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Dear Linux folks,


Am 22.03.22 um 19:27 schrieb Jakub Kicinski:
> On Tue, 22 Mar 2022 18:12:08 +0000 David Laight wrote:
>>>> Oh FFS why is that u16?
>>>> Don't do arithmetic on anything smaller than 'int'
>>>
>>> Any reasoning? I don't say it's good or bad, just want to hear your
>>> arguments (disasms, perf and object code measurements) etc.
>>
>> Look at the object code on anything except x86.
>> The compiler has to add instruction to mask the value
>> (which is in a full sized register) down to 16 bits
>> after every arithmetic operation.
> 
> Isn't it also slower on some modern x86 CPUs?
> I could have sworn someone mentioned that in the past.

I know of Scott’s article *Small Integers: Big Penalty* from 2012 [1].


Kind regards,

Paul


[1]: https://notabs.org/coding/smallIntsBigPenalty.htm
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