linux-kernel - Re: [PATCH v2 10/30] Add x86-specific parity functions

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Message-ID: <87wpoay10o.fsf@tassilo.jf.intel.com>
Date:	Wed, 06 Apr 2016 12:45:27 -0700
From:	Andi Kleen <andi@...stfloor.org>
To:	zengzhaoxiu@....com
Cc:	tglx@...utronix.de, mingo@...hat.com, hpa@...or.com,
	dvlasenk@...hat.com, bp@...e.de, akpm@...ux-foundation.org,
	dvyukov@...gle.com, keescook@...omium.org,
	linux-kernel@...r.kernel.org, Zhaoxiu Zeng <zhaoxiu.zeng@...il.com>
Subject: Re: [PATCH v2 10/30] Add x86-specific parity functions

zengzhaoxiu@....com writes:

> From: Zhaoxiu Zeng <zhaoxiu.zeng@...il.com>
>
> Use alternatives, lifted from arch_hweight

Is there actually anything performance critical in the kernel that uses
parity?

FWIW the arch hweight custom calling convention is a problem for LTO
because it needs different special flags, so I usually have to disable
it. Likely other reasonable usages, such as automatic source code
analysis, and other tool chain based usages have similar problems.

As far as I can tell both for hweight and likely for parity it is
badly overengineering and normal calling conventions would work as well,
and cause much less problems.

So if parity is really worth adding here (which I find doubtful,
but you may have numbers), please add it without these magic
calling hacks.

-Andi

-- 
ak@...ux.intel.com -- Speaking for myself only