linux-kernel - Re: [PATCH v3 1/2] x86, mwaitt: add monitorx and mwaitx instruction

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Message-ID: <20150611141904.GE30391@pd.tnic>
Date:	Thu, 11 Jun 2015 16:19:04 +0200
From:	Borislav Petkov <bp@...e.de>
To:	Huang Rui <ray.huang@....com>
Cc:	Andy Lutomirski <luto@...capital.net>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Len Brown <lenb@...nel.org>,
	John Stultz <john.stultz@...aro.org>,
	Frédéric Weisbecker <fweisbec@...il.com>,
	linux-kernel@...r.kernel.org, x86@...nel.org,
	Fengguang Wu <fengguang.wu@...el.com>,
	Aaron Lu <aaron.lu@...el.com>,
	Suravee Suthikulanit <suravee.suthikulpanit@....com>,
	Tony Li <tony.li@....com>, Ken Xue <ken.xue@....com>
Subject: Re: [PATCH v3 1/2] x86, mwaitt: add monitorx and mwaitx instruction

On Thu, Jun 11, 2015 at 10:14:10PM +0800, Huang Rui wrote:
> On AMD Carrizo processors (Family 15h, Model 60h-6fh), there is a new
> feature called MWAITT (Mwait with a timer) as an extension of
> Monitor/Mwait.
> 
> MWAITT, another name is MWAITX (MWAIT with extensions), has a configurable
> timer that causes MWAITX to exit on expiration.
> 
> Compared with MONITOR/MWAIT, there are minor differences in opcode and
> input parameters.
> 
> MWAITX ECX[1]: enable timer if set
> MWAITX EBX[31:0]: max wait time expressed in SW P0 clocks
> 
>                 MWAIT                           MWAITX
> opcode          0f 01 c9           |            0f 01 fb
> ECX[0]                  value of RFLAGS.IF seen by instruction
> ECX[1]          unused/#GP if set  |            enable timer if set
> ECX[31:2]                     unused/#GP if set
> EAX                           unused (reserve for hint)
> EBX[31:0]       unused             |            max wait time (loops)
> 
>                 MONITOR                         MONITORX
> opcode          0f 01 c8           |            0f 01 fa
> EAX                     (logical) address to monitor
> ECX                     #GP if not zero
> 
> The software P0 frequency is the same as the TSC frequency.
> 
> Max timeout = EBX/(TSC frequency)

As suggested last time, please put the description of MWAITX over
__mwaitx() in the code as comments below. See below.

> Signed-off-by: Huang Rui <ray.huang@....com>
> ---
>  arch/x86/include/asm/cpufeature.h |  1 +
>  arch/x86/include/asm/mwait.h      | 16 ++++++++++++++++
>  2 files changed, 17 insertions(+)
> 
> diff --git a/arch/x86/include/asm/cpufeature.h b/arch/x86/include/asm/cpufeature.h
> index 3d6606f..3ef1f6e 100644
> --- a/arch/x86/include/asm/cpufeature.h
> +++ b/arch/x86/include/asm/cpufeature.h
> @@ -176,6 +176,7 @@
>  #define X86_FEATURE_PERFCTR_NB  ( 6*32+24) /* NB performance counter extensions */
>  #define X86_FEATURE_BPEXT	(6*32+26) /* data breakpoint extension */
>  #define X86_FEATURE_PERFCTR_L2	( 6*32+28) /* L2 performance counter extensions */
> +#define X86_FEATURE_MWAITT	( 6*32+29) /* Mwait extension (MonitorX/MwaitX) */
>  
>  /*
>   * Auxiliary flags: Linux defined - For features scattered in various
> diff --git a/arch/x86/include/asm/mwait.h b/arch/x86/include/asm/mwait.h
> index 653dfa7..ece8048 100644
> --- a/arch/x86/include/asm/mwait.h
> +++ b/arch/x86/include/asm/mwait.h
> @@ -23,6 +23,14 @@ static inline void __monitor(const void *eax, unsigned long ecx,
>  		     :: "a" (eax), "c" (ecx), "d"(edx));
>  }
>  
> +static inline void __monitorx(const void *eax, unsigned long ecx,
> +			      unsigned long edx)
> +{
> +	/* "monitorx %eax, %ecx, %edx;" */
> +	asm volatile(".byte 0x0f, 0x01, 0xfa;"
> +		     :: "a" (eax), "c" (ecx), "d"(edx));
> +}
> +
>  static inline void __mwait(unsigned long eax, unsigned long ecx)
>  {
>  	/* "mwait %eax, %ecx;" */
> @@ -30,6 +38,14 @@ static inline void __mwait(unsigned long eax, unsigned long ecx)
>  		     :: "a" (eax), "c" (ecx));
>  }


<Add comment here!>

> +static inline void __mwaitx(unsigned long eax, unsigned long ebx,
> +			    unsigned long ecx)
> +{
> +	/* "mwaitx %eax, %ebx, %ecx;" */
> +	asm volatile(".byte 0x0f, 0x01, 0xfb;"
> +		     :: "a" (eax), "b" (ebx), "c" (ecx));
> +}
> +
>  static inline void __sti_mwait(unsigned long eax, unsigned long ecx)
>  {
>  	trace_hardirqs_on();
> -- 
> 1.9.1
> 

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.
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