Commit e8824890 authored by Thomas Gleixner's avatar Thomas Gleixner
Browse files

x86/delay: Preparatory code cleanup 



The naming conventions in the delay code are confusing at best.

All delay variants use a loops argument and or variable which originates
from the original delay_loop() implementation. But all variants except
delay_loop() are based on TSC cycles.

Rename the argument to cycles and make it type u64 to avoid these weird
expansions to u64 in the functions.

Rename MWAITX_MAX_LOOPS to MWAITX_MAX_WAIT_CYCLES for the same reason
and fixup the comment of delay_mwaitx() as well.

Mark the delay_fn function pointer __ro_after_init and fixup the comment
for it.

No functional change and preparation for the upcoming TPAUSE based delay
variant.

[ Kyung Min Park: Added __init to use_tsc_delay() ]

Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Signed-off-by: default avatarKyung Min Park <kyung.min.park@intel.com>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/1587757076-30337-2-git-send-email-kyung.min.park@intel.com
parent 3c40cdb0

arch/x86/include/asm/delay.h

+2 −1
Original line number Diff line number Diff line
@@ -3,8 +3,9 @@ 
#define _ASM_X86_DELAY_H



#include <asm-generic/delay.h>

#include <linux/init.h>



void use_tsc_delay(void);

void __init use_tsc_delay(void);

void use_mwaitx_delay(void);



#endif /* _ASM_X86_DELAY_H */

arch/x86/include/asm/mwait.h

+1 −1
Original line number Diff line number Diff line
@@ -20,7 +20,7 @@ 


#define MWAIT_ECX_INTERRUPT_BREAK	0x1

#define MWAITX_ECX_TIMER_ENABLE		BIT(1)

#define MWAITX_MAX_LOOPS		((u32)-1)

#define MWAITX_MAX_WAIT_CYCLES		UINT_MAX

#define MWAITX_DISABLE_CSTATES		0xf0



u32 get_umwait_control_msr(void);

arch/x86/lib/delay.c

+24 −21
Original line number Diff line number Diff line
@@ -27,9 +27,19 @@ 
# include <asm/smp.h>

#endif



static void delay_loop(u64 __loops);



/*

 * Calibration and selection of the delay mechanism happens only once

 * during boot.

 */

static void (*delay_fn)(u64) __ro_after_init = delay_loop;



/* simple loop based delay: */

static void delay_loop(unsigned long loops)

static void delay_loop(u64 __loops)

{

	unsigned long loops = (unsigned long)__loops;



	asm volatile(

		"	test %0,%0	\n"

		"	jz 3f		\n"
@@ -49,9 +59,9 @@ static void delay_loop(unsigned long loops) 
}



/* TSC based delay: */

static void delay_tsc(unsigned long __loops)

static void delay_tsc(u64 cycles)

{

	u64 bclock, now, loops = __loops;

	u64 bclock, now;

	int cpu;



	preempt_disable();
@@ -59,7 +69,7 @@ static void delay_tsc(unsigned long __loops) 
	bclock = rdtsc_ordered();

	for (;;) {

		now = rdtsc_ordered();

		if ((now - bclock) >= loops)

		if ((now - bclock) >= cycles)

			break;



		/* Allow RT tasks to run */
@@ -77,7 +87,7 @@ static void delay_tsc(unsigned long __loops) 
		 * counter for this CPU.

		 */

		if (unlikely(cpu != smp_processor_id())) {

			loops -= (now - bclock);

			cycles -= (now - bclock);

			cpu = smp_processor_id();

			bclock = rdtsc_ordered();

		}
@@ -87,24 +97,24 @@ static void delay_tsc(unsigned long __loops) 


/*

 * On some AMD platforms, MWAITX has a configurable 32-bit timer, that

 * counts with TSC frequency. The input value is the loop of the

 * counter, it will exit when the timer expires.

 * counts with TSC frequency. The input value is the number of TSC cycles

 * to wait. MWAITX will also exit when the timer expires.

 */

static void delay_mwaitx(unsigned long __loops)

static void delay_mwaitx(u64 cycles)

{

	u64 start, end, delay, loops = __loops;

	u64 start, end, delay;



	/*

	 * Timer value of 0 causes MWAITX to wait indefinitely, unless there

	 * is a store on the memory monitored by MONITORX.

	 */

	if (loops == 0)

	if (!cycles)

		return;



	start = rdtsc_ordered();



	for (;;) {

		delay = min_t(u64, MWAITX_MAX_LOOPS, loops);

		delay = min_t(u64, MWAITX_MAX_WAIT_CYCLES, cycles);



		/*

		 * Use cpu_tss_rw as a cacheline-aligned, seldomly
@@ -121,22 +131,15 @@ static void delay_mwaitx(unsigned long __loops) 


		end = rdtsc_ordered();



		if (loops <= end - start)

		if (cycles <= end - start)

			break;



		loops -= end - start;



		cycles -= end - start;

		start = end;

	}

}



/*

 * Since we calibrate only once at boot, this

 * function should be set once at boot and not changed

 */

static void (*delay_fn)(unsigned long) = delay_loop;



void use_tsc_delay(void)

void __init use_tsc_delay(void)

{

	if (delay_fn == delay_loop)

		delay_fn = delay_tsc;

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