X-Git-Url: http://git.liburcu.org/?a=blobdiff_plain;f=wrapper%2Ftrace-clock.h;h=08f99229225e6e870d5d78d13d0446f5cc357b0c;hb=refs%2Fheads%2Fstable-2.9;hp=496fec4360c7f654c18f454acae564ba43adabe7;hpb=7b9c008237e4bd47f9416cb8218def5f30d496ec;p=lttng-modules.git diff --git a/wrapper/trace-clock.h b/wrapper/trace-clock.h index 496fec43..08f99229 100644 --- a/wrapper/trace-clock.h +++ b/wrapper/trace-clock.h @@ -37,6 +37,7 @@ #include #include #include +#include #include #include @@ -59,65 +60,36 @@ extern struct lttng_trace_clock *lttng_trace_clock; #define LTTNG_CLOCK_NMI_SAFE_BROKEN #endif +/* + * We need clock values to be monotonically increasing per-cpu, which is + * not strictly guaranteed by ktime_get_mono_fast_ns(). It is + * straightforward to do on architectures with a 64-bit cmpxchg(), but + * not so on architectures without 64-bit cmpxchg. For now, only enable + * this feature on 64-bit architectures. + */ + #if (LINUX_VERSION_CODE >= KERNEL_VERSION(3,17,0) \ + && BITS_PER_LONG == 64 \ && !defined(LTTNG_CLOCK_NMI_SAFE_BROKEN)) +#define LTTNG_USE_NMI_SAFE_CLOCK +#endif -DECLARE_PER_CPU(local_t, lttng_last_tsc); +#ifdef LTTNG_USE_NMI_SAFE_CLOCK -#if (BITS_PER_LONG == 32) -/* - * Fixup "src_now" using the 32 LSB from "last". We need to handle overflow and - * underflow of the 32nd bit. "last" can be above, below or equal to the 32 LSB - * of "src_now". - */ -static inline u64 trace_clock_fixup(u64 src_now, u32 last) -{ - u64 now; - - now = src_now & 0xFFFFFFFF00000000ULL; - now |= (u64) last; - /* Detect overflow or underflow between now and last. */ - if ((src_now & 0x80000000U) && !(last & 0x80000000U)) { - /* - * If 32nd bit transitions from 1 to 0, and we move forward in - * time from "now" to "last", then we have an overflow. - */ - if (((s32) now - (s32) last) < 0) - now += 0x0000000100000000ULL; - } else if (!(src_now & 0x80000000U) && (last & 0x80000000U)) { - /* - * If 32nd bit transitions from 0 to 1, and we move backward in - * time from "now" to "last", then we have an underflow. - */ - if (((s32) now - (s32) last) > 0) - now -= 0x0000000100000000ULL; - } - return now; -} -#else /* #if (BITS_PER_LONG == 32) */ -/* - * The fixup is pretty easy on 64-bit architectures: "last" is a 64-bit - * value, so we can use last directly as current time. - */ -static inline u64 trace_clock_fixup(u64 src_now, u64 last) -{ - return last; -} -#endif /* #else #if (BITS_PER_LONG == 32) */ +DECLARE_PER_CPU(u64, lttng_last_tsc); /* * Sometimes called with preemption enabled. Can be interrupted. */ static inline u64 trace_clock_monotonic_wrapper(void) { - u64 now; - unsigned long last, result; - local_t *last_tsc; + u64 now, last, result; + u64 *last_tsc_ptr; /* Use fast nmi-safe monotonic clock provided by the Linux kernel. */ preempt_disable(); - last_tsc = lttng_this_cpu_ptr(<tng_last_tsc); - last = local_read(last_tsc); + last_tsc_ptr = lttng_this_cpu_ptr(<tng_last_tsc); + last = *last_tsc_ptr; /* * Read "last" before "now". It is not strictly required, but it ensures * that an interrupt coming in won't artificially trigger a case where @@ -126,9 +98,9 @@ static inline u64 trace_clock_monotonic_wrapper(void) */ barrier(); now = ktime_get_mono_fast_ns(); - if (((long) now - (long) last) < 0) - now = trace_clock_fixup(now, last); - result = local_cmpxchg(last_tsc, last, (unsigned long) now); + if (U64_MAX / 2 < now - last) + now = last; + result = cmpxchg64_local(last_tsc_ptr, last, now); preempt_enable(); if (result == last) { /* Update done. */ @@ -139,11 +111,11 @@ static inline u64 trace_clock_monotonic_wrapper(void) * "result", since it has been sampled concurrently with our * time read, so it should not be far from "now". */ - return trace_clock_fixup(now, result); + return result; } } -#else /* #if (LINUX_VERSION_CODE >= KERNEL_VERSION(3,17,0)) */ +#else /* #ifdef LTTNG_USE_NMI_SAFE_CLOCK */ static inline u64 trace_clock_monotonic_wrapper(void) { ktime_t ktime; @@ -158,7 +130,7 @@ static inline u64 trace_clock_monotonic_wrapper(void) ktime = ktime_get(); return ktime_to_ns(ktime); } -#endif /* #else #if (LINUX_VERSION_CODE >= KERNEL_VERSION(3,17,0)) */ +#endif /* #else #ifdef LTTNG_USE_NMI_SAFE_CLOCK */ static inline u64 trace_clock_read64_monotonic(void) { @@ -185,19 +157,19 @@ static inline const char *trace_clock_description_monotonic(void) return "Monotonic Clock"; } -#if (LINUX_VERSION_CODE >= KERNEL_VERSION(3,17,0)) +#ifdef LTTNG_USE_NMI_SAFE_CLOCK static inline int get_trace_clock(void) { printk_once(KERN_WARNING "LTTng: Using mainline kernel monotonic fast clock, which is NMI-safe.\n"); return 0; } -#else /* #if (LINUX_VERSION_CODE >= KERNEL_VERSION(3,17,0)) */ +#else /* #ifdef LTTNG_USE_NMI_SAFE_CLOCK */ static inline int get_trace_clock(void) { printk_once(KERN_WARNING "LTTng: Using mainline kernel monotonic clock. NMIs will not be traced.\n"); return 0; } -#endif /* #else #if (LINUX_VERSION_CODE >= KERNEL_VERSION(3,17,0)) */ +#endif /* #else #ifdef LTTNG_USE_NMI_SAFE_CLOCK */ static inline void put_trace_clock(void) { @@ -205,7 +177,7 @@ static inline void put_trace_clock(void) static inline u64 trace_clock_read64(void) { - struct lttng_trace_clock *ltc = ACCESS_ONCE(lttng_trace_clock); + struct lttng_trace_clock *ltc = READ_ONCE(lttng_trace_clock); if (likely(!ltc)) { return trace_clock_read64_monotonic(); @@ -217,7 +189,7 @@ static inline u64 trace_clock_read64(void) static inline u64 trace_clock_freq(void) { - struct lttng_trace_clock *ltc = ACCESS_ONCE(lttng_trace_clock); + struct lttng_trace_clock *ltc = READ_ONCE(lttng_trace_clock); if (!ltc) { return trace_clock_freq_monotonic(); @@ -229,7 +201,7 @@ static inline u64 trace_clock_freq(void) static inline int trace_clock_uuid(char *uuid) { - struct lttng_trace_clock *ltc = ACCESS_ONCE(lttng_trace_clock); + struct lttng_trace_clock *ltc = READ_ONCE(lttng_trace_clock); read_barrier_depends(); /* load ltc before content */ /* Use default UUID cb when NULL */ @@ -242,7 +214,7 @@ static inline int trace_clock_uuid(char *uuid) static inline const char *trace_clock_name(void) { - struct lttng_trace_clock *ltc = ACCESS_ONCE(lttng_trace_clock); + struct lttng_trace_clock *ltc = READ_ONCE(lttng_trace_clock); if (!ltc) { return trace_clock_name_monotonic(); @@ -254,7 +226,7 @@ static inline const char *trace_clock_name(void) static inline const char *trace_clock_description(void) { - struct lttng_trace_clock *ltc = ACCESS_ONCE(lttng_trace_clock); + struct lttng_trace_clock *ltc = READ_ONCE(lttng_trace_clock); if (!ltc) { return trace_clock_description_monotonic();