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

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Date:	Mon, 16 May 2016 12:19:15 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Peter Zijlstra <peterz@...radead.org>, 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>, x86@...nel.org,
	Denys Vlasenko <dvlasenk@...hat.com>
Subject: Re: [patch V4 09/31] bitops: Add x86-specific parity functions

On May 11, 2016 2:31:39 AM PDT, Peter Zijlstra <peterz@...radead.org> wrote:
>On Wed, May 11, 2016 at 05:16:38PM +0800, zengzhaoxiu@....com wrote:
>
>> +static inline unsigned int __arch_parity4(unsigned int w)
>> +{
>> +	unsigned int res = 0;
>> +
>> +	asm("test $0xf, %1; setpo %b0"
>> +		: "+q" (res)
>> +		: "r" (w)
>> +		: "cc");
>> +
>> +	return res;
>> +}
>> +
>> +static inline unsigned int __arch_parity8(unsigned int w)
>> +{
>> +	unsigned int res = 0;
>> +
>> +	asm("test %1, %1; setpo %b0"
>> +		: "+q" (res)
>> +		: "r" (w)
>> +		: "cc");
>> +
>> +	return res;
>> +}
>> +
>> +static inline unsigned int __arch_parity16(unsigned int w)
>> +{
>> +	unsigned int res = 0;
>> +
>> +	asm("xor %h1, %b1; setpo %b0"
>> +		: "+q" (res), "+q" (w)
>> +		: : "cc");
>> +
>> +	return res;
>> +}
>
>Please use the GEN_*_RMWcc() stuff to avoid the setpo where possible.
>
>> +
>> +#ifdef CONFIG_64BIT
>> +/* popcnt %eax, %eax -- redundant REX prefix for alignment */
>> +#define POPCNT32 ".byte 0xf3,0x40,0x0f,0xb8,0xc0"
>> +/* popcnt %rax, %rax */
>> +#define POPCNT64 ".byte 0xf3,0x48,0x0f,0xb8,0xc0"
>> +#else
>> +/* popcnt %eax, %eax */
>> +#define POPCNT32 ".byte 0xf3,0x0f,0xb8,0xc0"
>> +#endif
>
>Yuck, please don't duplicate stuff like this.
>
>> +
>> +static __always_inline unsigned int __arch_parity32(unsigned int w)
>> +{
>> +	unsigned int res;
>> +	unsigned int tmp;
>> +
>> +	asm(ALTERNATIVE(
>> +		"	mov	%%eax, %1	\n"
>> +		"	shr	$16, %%eax	\n"
>> +		"	xor	%1, %%eax	\n"
>> +		"	xor	%%ah, %%al	\n"
>> +		"	mov	$0, %%eax	\n"
>> +		"	setpo	%%al	\n",
>> +		POPCNT32 "			\n"
>> +		"	and	$1, %%eax	\n",
>> +		X86_FEATURE_POPCNT)
>> +		: "=a" (res), "=&r" (tmp)
>> +		: "a" (w)
>> +		: "cc");
>> +
>> +	return res;
>> +}
>
>How many bytes does that end up being? Should we make it a call?

Also, setxx is used with a "bool" or "u8", not " unsigned int"!!!!
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