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Diffstat (limited to 'arch/x86/lib/delay.c')
-rw-r--r--arch/x86/lib/delay.c114
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)