linux-kernel - Re: [PATCH v5 1/2] x86, mwaitt: add monitorx and mwaitx instruction

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Date:	Mon, 15 Jun 2015 12:55:42 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Huang Rui <ray.huang@....com>
Cc:	Borislav Petkov <bp@...e.de>,
	Andy Lutomirski <luto@...capital.net>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...nel.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 v5 1/2] x86, mwaitt: add monitorx and mwaitx instruction

On Mon, Jun 15, 2015 at 06:48:03PM +0800, Huang Rui wrote:
> +/*
> + * MWAITT allows for both a timer value to get you out of the MWAIT as
> + * well as the normal exit conditions.
> + *
> + * MWAITX ECX[1]: enable timer if set
> + * MWAITX EBX[31:0]: max wait time expressed in SW P0 clocks
> + *
> + * Below is the compared data between MWAIT and MWAITX on AMD
> + * processors:
> + *                 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)

Seeing how you're stuffing a !0 value in here in the next patch, the
above comment seems slightly incorrect, no?

> + * 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.
> + */
> +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
> 
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