diff options
Diffstat (limited to 'arch/x86/lib/delay.c')
| -rw-r--r-- | arch/x86/lib/delay.c | 114 |
1 files changed, 78 insertions, 36 deletions
diff --git a/arch/x86/lib/delay.c b/arch/x86/lib/delay.c index c126571e5e2e..65d15df6212d 100644 --- a/arch/x86/lib/delay.c +++ b/arch/x86/lib/delay.c @@ -27,9 +27,20 @@ # 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; +static void (*delay_halt_fn)(u64 start, u64 cycles) __ro_after_init; + /* 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 +60,9 @@ 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 +70,7 @@ 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 +88,7 @@ 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(); } @@ -86,65 +97,96 @@ static void delay_tsc(unsigned long __loops) } /* + * On Intel the TPAUSE instruction waits until any of: + * 1) the TSC counter exceeds the value provided in EDX:EAX + * 2) global timeout in IA32_UMWAIT_CONTROL is exceeded + * 3) an external interrupt occurs + */ +static void delay_halt_tpause(u64 start, u64 cycles) +{ + u64 until = start + cycles; + u32 eax, edx; + + eax = lower_32_bits(until); + edx = upper_32_bits(until); + + /* + * Hard code the deeper (C0.2) sleep state because exit latency is + * small compared to the "microseconds" that usleep() will delay. + */ + __tpause(TPAUSE_C02_STATE, edx, eax); +} + +/* * 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_halt_mwaitx(u64 unused, u64 cycles) { - u64 start, end, delay, loops = __loops; + u64 delay; + + delay = min_t(u64, MWAITX_MAX_WAIT_CYCLES, cycles); + /* + * Use cpu_tss_rw as a cacheline-aligned, seldomly accessed per-cpu + * variable as the monitor target. + */ + __monitorx(raw_cpu_ptr(&cpu_tss_rw), 0, 0); + + /* + * AMD, like Intel, supports the EAX hint and EAX=0xf means, do not + * enter any deep C-state and we use it here in delay() to minimize + * wakeup latency. + */ + __mwaitx(MWAITX_DISABLE_CSTATES, delay, MWAITX_ECX_TIMER_ENABLE); +} + +/* + * Call a vendor specific function to delay for a given amount of time. Because + * these functions may return earlier than requested, check for actual elapsed + * time and call again until done. + */ +static void delay_halt(u64 __cycles) +{ + u64 start, end, cycles = __cycles; /* * 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); - - /* - * Use cpu_tss_rw as a cacheline-aligned, seldomly - * accessed per-cpu variable as the monitor target. - */ - __monitorx(raw_cpu_ptr(&cpu_tss_rw), 0, 0); - - /* - * AMD, like Intel's MWAIT version, supports the EAX hint and - * EAX=0xf0 means, do not enter any deep C-state and we use it - * here in delay() to minimize wakeup latency. - */ - __mwaitx(MWAITX_DISABLE_CSTATES, delay, MWAITX_ECX_TIMER_ENABLE); - + delay_halt_fn(start, cycles); 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; } +void __init use_tpause_delay(void) +{ + delay_halt_fn = delay_halt_tpause; + delay_fn = delay_halt; +} + void use_mwaitx_delay(void) { - delay_fn = delay_mwaitx; + delay_halt_fn = delay_halt_mwaitx; + delay_fn = delay_halt; } int read_current_timer(unsigned long *timer_val) |