diff options
Diffstat (limited to 'usr/src/uts/i86pc/os/timestamp.c')
| -rw-r--r-- | usr/src/uts/i86pc/os/timestamp.c | 49 |
1 files changed, 49 insertions, 0 deletions
diff --git a/usr/src/uts/i86pc/os/timestamp.c b/usr/src/uts/i86pc/os/timestamp.c index 5b97d20e52..c40159018c 100644 --- a/usr/src/uts/i86pc/os/timestamp.c +++ b/usr/src/uts/i86pc/os/timestamp.c @@ -24,6 +24,7 @@ * Use is subject to license terms. * * Copyright 2012 Nexenta Systems, Inc. All rights reserved. + * Copyright (c) 2014, 2016 by Delphix. All rights reserved. */ #include <sys/types.h> @@ -45,6 +46,7 @@ #include <sys/time.h> #include <sys/panic.h> #include <sys/cpu.h> +#include <sys/sdt.h> /* * Using the Pentium's TSC register for gethrtime() @@ -151,6 +153,14 @@ static hrtime_t tsc_last = 0; static hrtime_t tsc_last_jumped = 0; static hrtime_t tsc_hrtime_base = 0; static int tsc_jumped = 0; +static uint32_t tsc_wayback = 0; +/* + * The cap of 1 second was chosen since it is the frequency at which the + * tsc_tick() function runs which means that when gethrtime() is called it + * should never be more than 1 second since tsc_last was updated. + */ +static hrtime_t tsc_resume_cap; +static hrtime_t tsc_resume_cap_ns = NANOSEC; /* 1s */ static hrtime_t shadow_tsc_hrtime_base; static hrtime_t shadow_tsc_last; @@ -158,6 +168,17 @@ static uint_t shadow_nsec_scale; static uint32_t shadow_hres_lock; int get_tsc_ready(); +static inline +hrtime_t tsc_protect(hrtime_t a) { + if (a > tsc_resume_cap) { + atomic_inc_32(&tsc_wayback); + DTRACE_PROBE3(tsc__wayback, htrime_t, a, hrtime_t, tsc_last, + uint32_t, tsc_wayback); + return (tsc_resume_cap); + } + return (a); +} + hrtime_t tsc_gethrtime(void) { @@ -186,6 +207,20 @@ tsc_gethrtime(void) * delta to be zero. */ tsc = 0; + } else { + /* + * If we reach this else clause we assume that we have + * gone through a suspend/resume cycle and use the + * current tsc value as the delta. + * + * In rare cases we can reach this else clause due to + * a lack of monotonicity in the TSC value. In such + * cases using the current TSC value as the delta would + * cause us to return a value ~2x of what it should + * be. To protect against these cases we cap the + * suspend/resume delta at tsc_resume_cap. + */ + tsc = tsc_protect(tsc); } hrt = tsc_hrtime_base; @@ -226,6 +261,8 @@ tsc_gethrtime_delta(void) tsc -= tsc_last; } else if (tsc >= tsc_last - 2 * tsc_max_delta) { tsc = 0; + } else { + tsc = tsc_protect(tsc); } hrt = tsc_hrtime_base; @@ -285,6 +322,8 @@ dtrace_gethrtime(void) tsc -= tsc_last; else if (tsc >= tsc_last - 2*tsc_max_delta) tsc = 0; + else + tsc = tsc_protect(tsc); hrt = tsc_hrtime_base; @@ -332,6 +371,8 @@ dtrace_gethrtime(void) tsc -= shadow_tsc_last; else if (tsc >= shadow_tsc_last - 2 * tsc_max_delta) tsc = 0; + else + tsc = tsc_protect(tsc); hrt = shadow_tsc_hrtime_base; @@ -598,6 +639,7 @@ tsc_tick(void) * resume (i.e nsec_scale remains the same). */ delta = now; + delta = tsc_protect(delta); tsc_last_jumped += tsc_last; tsc_jumped = 1; } else { @@ -650,6 +692,13 @@ tsc_hrtimeinit(uint64_t cpu_freq_hz) * This structure should be aligned on a multiple of cache line size. */ tscp = kmem_zalloc(PAGESIZE, KM_SLEEP); + + /* + * Convert the TSC resume cap ns value into its unscaled TSC value. + * See tsc_gethrtime(). + */ + if (tsc_resume_cap == 0) + TSC_CONVERT(tsc_resume_cap_ns, tsc_resume_cap, nsec_unscale); } int |