X-Git-Url: http://git.liburcu.org/?a=blobdiff_plain;f=wrapper%2Ftrace-clock.h;h=561094b3ae924a6545cf795f0ba838040c1273fe;hb=4f8399617e18698100e8ca4dc221ccd9e0f72e9f;hp=bced61c25aa8dfb1b7ec732e96f20037fa685205;hpb=cfaf9f3d3f9884557cd87f900bc5a0b353917b2b;p=lttng-modules.git diff --git a/wrapper/trace-clock.h b/wrapper/trace-clock.h index bced61c2..561094b3 100644 --- a/wrapper/trace-clock.h +++ b/wrapper/trace-clock.h @@ -32,8 +32,102 @@ #include #include #include +#include +#include +#include +#include "../lttng-kernel-version.h" +#include "percpu-defs.h" #include "random.h" +#if ((LTTNG_KERNEL_RANGE(3,10,0, 3,10,14) && !LTTNG_RHEL_KERNEL_RANGE(3,10,0,7,0, 3,10,14,0,0)) \ + || LTTNG_KERNEL_RANGE(3,11,0, 3,11,3)) +#error "Linux kernels 3.10 and 3.11 introduce a deadlock in the timekeeping subsystem. Fixed by commit 7bd36014460f793c19e7d6c94dab67b0afcfcb7f \"timekeeping: Fix HRTICK related deadlock from ntp lock changes\" in Linux." +#endif + +#if (LINUX_VERSION_CODE >= KERNEL_VERSION(3,17,0)) + +DECLARE_PER_CPU(local_t, lttng_last_tsc); + +#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) */ + +/* + * 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; + + /* 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); + /* + * Read "last" before "now". It is not strictly required, but it ensures + * that an interrupt coming in won't artificially trigger a case where + * "now" < "last". This kind of situation should only happen if the + * mono_fast time source goes slightly backwards. + */ + 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); + preempt_enable(); + if (result == last) { + /* Update done. */ + return now; + } else { + /* + * Update not done, due to concurrent update. We can use + * "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); + } +} + +#else /* #if (LINUX_VERSION_CODE >= KERNEL_VERSION(3,17,0)) */ static inline u64 trace_clock_monotonic_wrapper(void) { ktime_t ktime; @@ -48,11 +142,7 @@ static inline u64 trace_clock_monotonic_wrapper(void) ktime = ktime_get(); return ktime_to_ns(ktime); } - -static inline u32 trace_clock_read32(void) -{ - return (u32) trace_clock_monotonic_wrapper(); -} +#endif /* #else #if (LINUX_VERSION_CODE >= KERNEL_VERSION(3,17,0)) */ static inline u64 trace_clock_read64(void) { @@ -69,23 +159,19 @@ static inline int trace_clock_uuid(char *uuid) return wrapper_get_bootid(uuid); } +#if (LINUX_VERSION_CODE >= KERNEL_VERSION(3,17,0)) static inline int get_trace_clock(void) { - /* - * LTTng: Using mainline kernel monotonic clock. NMIs will not be - * traced, and expect significant performance degradation compared to - * the LTTng trace clocks. Integration of the LTTng 0.x trace clocks - * into LTTng 2.0 is planned in a near future. - */ - printk(KERN_WARNING "LTTng: Using mainline kernel monotonic clock.\n"); - printk(KERN_WARNING " * NMIs will not be traced,\n"); - printk(KERN_WARNING " * expect significant performance degradation compared to the\n"); - printk(KERN_WARNING " LTTng trace clocks.\n"); - printk(KERN_WARNING "Integration of the LTTng 0.x trace clocks into LTTng 2.0 is planned\n"); - printk(KERN_WARNING "in a near future.\n"); - + printk(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)) */ +static inline int get_trace_clock(void) +{ + printk(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)) */ static inline void put_trace_clock(void) {