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kernel: use monitor/mwait instruction on pc multiprocessor for idlehands

--- a/sys/src/9/pc/dat.h

+++ b/sys/src/9/pc/dat.h

@@ -218,6 +218,7 @@

 	uvlong	cyclefreq;		/* Frequency of user readable cycle counter */

 	uvlong	cpuhz;

 	int	cpuidax;

+	int	cpuidcx;

 	int	cpuiddx;

 	char	cpuidid[16];

 	char*	cpuidtype;

@@ -277,6 +278,9 @@

 /* cpuid instruction result register bits */

 enum {

+	/* cx */

+	Monitor	= 1<<3,

+

 	/* dx */

 	Fpuonchip = 1<<0,

 //	Pse	= 1<<3,		/* page size extensions */

--- a/sys/src/9/pc/devarch.c

+++ b/sys/src/9/pc/devarch.c

@@ -732,8 +732,8 @@

 	if(m->cpuidid[0])

 		i += sprint(buf+i, "%12.12s ", m->cpuidid);

 	seprint(buf+i, buf + sizeof buf - 1,

-		"%s (cpuid: AX 0x%4.4uX DX 0x%4.4uX)\n",

-		m->cpuidtype, m->cpuidax, m->cpuiddx);

+		"%s (cpuid: AX 0x%4.4uX CX 0x%4.4uX DX 0x%4.4uX)\n",

+		m->cpuidtype, m->cpuidax, m->cpuidcx, m->cpuiddx);

 	print(buf);

 }

@@ -766,6 +766,7 @@

 	cpuid(Procsig, regs);

 	m->cpuidax = regs[0];

+	m->cpuidcx = regs[2];

 	m->cpuiddx = regs[3];

 	if(strncmp(m->cpuidid, "AuthenticAMD", 12) == 0 ||

--- a/sys/src/9/pc/fns.h

+++ b/sys/src/9/pc/fns.h

@@ -42,6 +42,7 @@

 char*	getconf(char*);

 void	guesscpuhz(int);

 void	halt(void);

+void	mwait(void*);

 int	i8042auxcmd(int);

 int	i8042auxcmds(uchar*, int);

 void	i8042auxenable(void (*)(int, int));

--- a/sys/src/9/pc/l.s

+++ b/sys/src/9/pc/l.s

@@ -855,6 +855,21 @@

 	HLT

 	RET

+TEXT mwait(SB), $0

+	MOVL	addr+0(FP), AX

+	MOVL	(AX), CX

+	ORL	CX, CX

+	JNZ	_mwaitdone

+	XORL	DX, DX

+	BYTE $0x0f; BYTE $0x01; BYTE $0xc8	/* MONITOR */

+	MOVL	(AX), CX

+	ORL	CX, CX

+	JNZ	_mwaitdone

+	XORL	AX, AX

+	BYTE $0x0f; BYTE $0x01; BYTE $0xc9	/* MWAIT */

+_mwaitdone:

+	RET

+

 /*

  * Interrupt/exception handling.

  * Each entry in the vector table calls either _strayintr or _strayintrx depending

--- a/sys/src/9/pc/main.c

+++ b/sys/src/9/pc/main.c

@@ -868,6 +868,10 @@

 void

 idlehands(void)

 {

+	extern int nrdy;

+

 	if(conf.nmach == 1)

 		halt();

+	else if(m->cpuidcx & Monitor)

+		mwait(&nrdy);

 }

-- 

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