This patch makes the vDSO handle clock_gettime(CLOCK_MONOTONIC_RAW,&ts) calls in the same way it handles clock_gettime(CLOCK_MONOTONIC,&ts) calls, reducing latency from @ 200-1000ns to @ 20ns.
It has been resent and augmented to support compilation with -DRETPOLINE / -mindirect-branch=thunk-extern -mindirect-branch-register, to avoid generating relocations for thunks. --- diff --git a/arch/x86/entry/vdso/vclock_gettime.c b/arch/x86/entry/vdso/vclock_gettime.c index f19856d..9b89f86 100644 --- a/arch/x86/entry/vdso/vclock_gettime.c +++ b/arch/x86/entry/vdso/vclock_gettime.c @@ -182,29 +182,60 @@ notrace static u64 vread_tsc(void) return last; } -notrace static inline u64 vgetsns(int *mode) +notrace static inline u64 vgetcycles(int *mode) { - u64 v; - cycles_t cycles; - - if (gtod->vclock_mode == VCLOCK_TSC) - cycles = vread_tsc(); + switch (gtod->vclock_mode) { + case VCLOCK_TSC: + return vread_tsc(); #ifdef CONFIG_PARAVIRT_CLOCK - else if (gtod->vclock_mode == VCLOCK_PVCLOCK) - cycles = vread_pvclock(mode); + case VCLOCK_PVCLOCK: + return vread_pvclock(mode); #endif #ifdef CONFIG_HYPERV_TSCPAGE - else if (gtod->vclock_mode == VCLOCK_HVCLOCK) - cycles = vread_hvclock(mode); + case VCLOCK_HVCLOCK: + return vread_hvclock(mode); #endif - else + default: + break; + } + return 0; +} + +notrace static inline u64 vgetsns(int *mode) +{ + u64 v; + cycles_t cycles = vgetcycles(mode); + + if (cycles == 0) return 0; + v = (cycles - gtod->cycle_last) & gtod->mask; return v * gtod->mult; } +notrace static inline u64 vgetsns_raw(int *mode) +{ + u64 v; + cycles_t cycles = vgetcycles(mode); + + if (cycles == 0) + return 0; + + v = (cycles - gtod->cycle_last) & gtod->mask; + return v * gtod->raw_mult; +} + +#ifdef RETPOLINE +# define _NO_THUNK_RELOCS_()(indirect_branch("keep"),\ + function_return("keep")) +# define _RETPOLINE_FUNC_ATTR_ __attribute__(_NO_THUNK_RELOCS_()) +#else +# define _RETPOLINE_FUNC_ATTR_ +#endif + /* Code size doesn't matter (vdso is 4k anyway) and this is faster. */ -notrace static int __always_inline do_realtime(struct timespec *ts) +notrace static inline _RETPOLINE_FUNC_ATTR_ +int do_realtime(struct timespec *ts) { unsigned long seq; u64 ns; @@ -225,7 +256,8 @@ notrace static int __always_inline do_realtime(struct timespec *ts) return mode; } -notrace static int __always_inline do_monotonic(struct timespec *ts) +notrace static inline _RETPOLINE_FUNC_ATTR_ +int do_monotonic(struct timespec *ts) { unsigned long seq; u64 ns; @@ -246,7 +278,30 @@ notrace static int __always_inline do_monotonic(struct timespec *ts) return mode; } -notrace static void do_realtime_coarse(struct timespec *ts) +notrace static inline _RETPOLINE_FUNC_ATTR_ +int do_monotonic_raw(struct timespec *ts) +{ + unsigned long seq; + u64 ns; + int mode; + + do { + seq = gtod_read_begin(gtod); + mode = gtod->vclock_mode; + ts->tv_sec = gtod->monotonic_time_raw_sec; + ns = gtod->monotonic_time_raw_nsec; + ns += vgetsns_raw(&mode); + ns >>= gtod->raw_shift; + } while (unlikely(gtod_read_retry(gtod, seq))); + + ts->tv_sec += __iter_div_u64_rem(ns, NSEC_PER_SEC, &ns); + ts->tv_nsec = ns; + + return mode; +} + +notrace static inline _RETPOLINE_FUNC_ATTR_ +void do_realtime_coarse(struct timespec *ts) { unsigned long seq; do { @@ -256,7 +311,8 @@ notrace static void do_realtime_coarse(struct timespec *ts) } while (unlikely(gtod_read_retry(gtod, seq))); } -notrace static void do_monotonic_coarse(struct timespec *ts) +notrace static inline _RETPOLINE_FUNC_ATTR_ +void do_monotonic_coarse(struct timespec *ts) { unsigned long seq; do { @@ -266,7 +322,11 @@ notrace static void do_monotonic_coarse(struct timespec *ts) } while (unlikely(gtod_read_retry(gtod, seq))); } -notrace int __vdso_clock_gettime(clockid_t clock, struct timespec *ts) +notrace +#ifdef RETPOLINE + __attribute__((indirect_branch("keep"), function_return("keep"))) +#endif +int __vdso_clock_gettime(clockid_t clock, struct timespec *ts) { switch (clock) { case CLOCK_REALTIME: @@ -277,6 +337,10 @@ notrace int __vdso_clock_gettime(clockid_t clock, struct timespec *ts) if (do_monotonic(ts) == VCLOCK_NONE) goto fallback; break; + case CLOCK_MONOTONIC_RAW: + if (do_monotonic_raw(ts) == VCLOCK_NONE) + goto fallback; + break; case CLOCK_REALTIME_COARSE: do_realtime_coarse(ts); break; diff --git a/arch/x86/entry/vsyscall/vsyscall_gtod.c b/arch/x86/entry/vsyscall/vsyscall_gtod.c index e1216dd..c4d89b6 100644 --- a/arch/x86/entry/vsyscall/vsyscall_gtod.c +++ b/arch/x86/entry/vsyscall/vsyscall_gtod.c @@ -44,6 +44,8 @@ void update_vsyscall(struct timekeeper *tk) vdata->mask = tk->tkr_mono.mask; vdata->mult = tk->tkr_mono.mult; vdata->shift = tk->tkr_mono.shift; + vdata->raw_mult = tk->tkr_raw.mult; + vdata->raw_shift = tk->tkr_raw.shift; vdata->wall_time_sec = tk->xtime_sec; vdata->wall_time_snsec = tk->tkr_mono.xtime_nsec; @@ -74,5 +76,8 @@ void update_vsyscall(struct timekeeper *tk) vdata->monotonic_time_coarse_sec++; } + vdata->monotonic_time_raw_sec = tk->raw_sec; + vdata->monotonic_time_raw_nsec = tk->tkr_raw.xtime_nsec; + gtod_write_end(vdata); } diff --git a/arch/x86/include/asm/vgtod.h b/arch/x86/include/asm/vgtod.h index fb856c9..ec1a37c 100644 --- a/arch/x86/include/asm/vgtod.h +++ b/arch/x86/include/asm/vgtod.h @@ -22,7 +22,8 @@ struct vsyscall_gtod_data { u64 mask; u32 mult; u32 shift; - + u32 raw_mult; + u32 raw_shift; /* open coded 'struct timespec' */ u64 wall_time_snsec; gtod_long_t wall_time_sec; @@ -32,6 +33,8 @@ struct vsyscall_gtod_data { gtod_long_t wall_time_coarse_nsec; gtod_long_t monotonic_time_coarse_sec; gtod_long_t monotonic_time_coarse_nsec; + gtod_long_t monotonic_time_raw_sec; + gtod_long_t monotonic_time_raw_nsec; int tz_minuteswest; int tz_dsttime;