diff options
| -rw-r--r-- | arch/x86/include/asm/vdso/gettimeofday.h | 27 | ||||
| -rw-r--r-- | lib/vdso/gettimeofday.c | 19 |
2 files changed, 42 insertions, 4 deletions
diff --git a/arch/x86/include/asm/vdso/gettimeofday.h b/arch/x86/include/asm/vdso/gettimeofday.h index 5b63f1f78a1f..a14039a59abd 100644 --- a/arch/x86/include/asm/vdso/gettimeofday.h +++ b/arch/x86/include/asm/vdso/gettimeofday.h @@ -229,6 +229,33 @@ static __always_inline const struct vdso_data *__arch_get_vdso_data(void) return __vdso_data; } +/* + * x86 specific delta calculation. + * + * The regular implementation assumes that clocksource reads are globally + * monotonic. The TSC can be slightly off across sockets which can cause + * the regular delta calculation (@cycles - @last) to return a huge time + * jump. + * + * Therefore it needs to be verified that @cycles are greater than + * @last. If not then use @last, which is the base time of the current + * conversion period. + * + * This variant also removes the masking of the subtraction because the + * clocksource mask of all VDSO capable clocksources on x86 is U64_MAX + * which would result in a pointless operation. The compiler cannot + * optimize it away as the mask comes from the vdso data and is not compile + * time constant. + */ +static __always_inline +u64 vdso_calc_delta(u64 cycles, u64 last, u64 mask, u32 mult) +{ + if (cycles > last) + return (cycles - last) * mult; + return 0; +} +#define vdso_calc_delta vdso_calc_delta + #endif /* !__ASSEMBLY__ */ #endif /* __ASM_VDSO_GETTIMEOFDAY_H */ diff --git a/lib/vdso/gettimeofday.c b/lib/vdso/gettimeofday.c index ef28cc5d7bff..2d1c1f241fd9 100644 --- a/lib/vdso/gettimeofday.c +++ b/lib/vdso/gettimeofday.c @@ -26,6 +26,18 @@ #include <asm/vdso/gettimeofday.h> #endif /* ENABLE_COMPAT_VDSO */ +#ifndef vdso_calc_delta +/* + * Default implementation which works for all sane clocksources. That + * obviously excludes x86/TSC. + */ +static __always_inline +u64 vdso_calc_delta(u64 cycles, u64 last, u64 mask, u32 mult) +{ + return ((cycles - last) & mask) * mult; +} +#endif + static int do_hres(const struct vdso_data *vd, clockid_t clk, struct __kernel_timespec *ts) { @@ -35,14 +47,13 @@ static int do_hres(const struct vdso_data *vd, clockid_t clk, do { seq = vdso_read_begin(vd); - cycles = __arch_get_hw_counter(vd->clock_mode) & - vd->mask; + cycles = __arch_get_hw_counter(vd->clock_mode); ns = vdso_ts->nsec; last = vd->cycle_last; if (unlikely((s64)cycles < 0)) return clock_gettime_fallback(clk, ts); - if (cycles > last) - ns += (cycles - last) * vd->mult; + + ns += vdso_calc_delta(cycles, last, vd->mask, vd->mult); ns >>= vd->shift; sec = vdso_ts->sec; } while (unlikely(vdso_read_retry(vd, seq))); |