linux-kernel - Re: [patch V4 09/31] bitops: Add x86-specific parity functions

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Message-ID: <20160516170608.GV3192@twins.programming.kicks-ass.net>
Date:	Mon, 16 May 2016 19:06:08 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Zhaoxiu Zeng <zengzhaoxiu@....com>
Cc:	linux-kernel@...r.kernel.org, bp@...e.de,
	gnomes@...rguk.ukuu.org.uk, andi@...stfloor.org,
	dvyukov@...gle.com, Zhaoxiu Zeng <zhaoxiu.zeng@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
	Denys Vlasenko <dvlasenk@...hat.com>
Subject: Re: [patch V4 09/31] bitops: Add x86-specific parity functions

On Mon, May 16, 2016 at 11:49:05PM +0800, Zhaoxiu Zeng wrote:
> On 2016/5/11 17:31, Peter Zijlstra wrote:
> > Please use the GEN_*_RMWcc() stuff to avoid the setpo where possible.
> 
> Setpo is better.
> In most cases, we need to store the parity, or compare it with other variables.
> 
> For example, in drivers/net/ethernet/broadcom/tg3.c,
> 
> static int tg3_test_nvram(struct tg3 *tp)
> {
> 	......
> 	if (parity8(data[i]) == !!parity[i])
> 		goto out;
> 	......
> }
> 
> If use GEN_BINARY_RMWcc stuff，
> 
> static inline unsigned int __arch_parity8(unsigned int w)
> {
> 	GEN_BINARY_RMWcc("testb", w, "er", 0xff, "%0", "po");
> }

blergh; GCC does indeed make a mess of that. It looks we'll need the
cc-output stuff for this in order for GCC to generates sane code for
that :/