linux-kernel - Re: [RFC PATCH 1/4] x86, mwaitt: add monitorx and mwaitx instruction

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Date:	Tue, 19 May 2015 13:29:45 +0200
From:	Borislav Petkov <bp@...e.de>
To:	Huang Rui <ray.huang@....com>
Cc:	Len Brown <lenb@...nel.org>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Thomas Gleixner <tglx@...utronix.de>, x86@...nel.org,
	linux-kernel@...r.kernel.org,
	Fengguang Wu <fengguang.wu@...el.com>,
	Aaron Lu <aaron.lu@...el.com>, Tony Li <tony.li@....com>
Subject: Re: [RFC PATCH 1/4] x86, mwaitt: add monitorx and mwaitx instruction

On Tue, May 19, 2015 at 04:01:09PM +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

What's the behavior if you set EBX to some value but don't enable the
timer with ECX? Normal MWAIT?

> The software P0 frequency is the same as the TSC frequency.
> 
> Max timeout = EBX/(TSC frequency)

That's max timeout in seconds then.

> Signed-off-by: Huang Rui <ray.huang@....com>
> ---
>  arch/x86/include/asm/cpufeature.h |  1 +
>  arch/x86/include/asm/mwait.h      | 25 +++++++++++++++++++++++++
>  2 files changed, 26 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..b91136f 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;"

Ah ok, ModRM extension to secondary opcode 0x1. Simply filling out the
empty slots after SWAPGS, RDTSCP, ... :)

> +		     :: "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));
>  }
>  
> +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();
> @@ -38,6 +54,15 @@ static inline void __sti_mwait(unsigned long eax, unsigned long ecx)
>  		     :: "a" (eax), "c" (ecx));
>  }
>  
> +static inline void __sti_mwaitx(unsigned long eax, unsigned long ebx,
> +		unsigned long ecx)

Please align the argument on the new line to the opening brace:

static inline void __sti_mwaitx(unsigned long eax, unsigned long ebx,
				unsigned long ecx)

> +{
> +	trace_hardirqs_on();
> +	/* "mwaitx %eax, %ebx, %ecx;" */
> +	asm volatile("sti; .byte 0x0f, 0x01, 0xfb;"
> +		     :: "a" (eax), "b" (ebx), "c" (ecx));
> +}
> +
>  /*
>   * This uses new MONITOR/MWAIT instructions on P4 processors with PNI,
>   * which can obviate IPI to trigger checking of need_resched.
> -- 
> 2.1.0
> 

-- 
Regards/Gruss,
    Boris.

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