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11585 ::scalehrtime could be more precise
Reviewed by: Jerry Jelinek <jerry.jelinek@joyent.com>
*** 768,777 ****
--- 768,797 ----
"rooted at the given cr3 value / physical address.\n"
"\n"
"-w run ::whatis on mapping start addresses\n");
}
+ static const char *const scalehrtime_desc =
+ "Scales a timestamp from ticks to nanoseconds. Unscaled timestamps\n"
+ "are used as both a quick way of accumulating relative time (as for\n"
+ "usage) and as a quick way of getting the absolute current time.\n"
+ "These uses require slightly different scaling algorithms. By\n"
+ "default, if a specified time is greater than half of the unscaled\n"
+ "time at the last tick (that is, if the unscaled time represents\n"
+ "more than half the time since boot), the timestamp is assumed to\n"
+ "be absolute, and the scaling algorithm used mimics that which the\n"
+ "kernel uses in gethrtime(). Otherwise, the timestamp is assumed to\n"
+ "be relative, and the algorithm mimics scalehrtime(). This behavior\n"
+ "can be overridden by forcing the unscaled time to be interpreted\n"
+ "as relative (via -r) or absolute (via -a).\n";
+
+ static void
+ scalehrtime_help(void)
+ {
+ mdb_printf("%s", scalehrtime_desc);
+ }
+
/*
* NSEC_SHIFT is replicated here (it is not defined in a header file),
* but for amusement, the reader is directed to the comment that explains
* the rationale for this particular value on x86. Spoiler: the value is
* selected to accommodate 60 MHz Pentiums! (And a confession: if the voice
*** 783,808 ****
/*ARGSUSED*/
static int
scalehrtime_cmd(uintptr_t addr, uint_t flags, int argc, const mdb_arg_t *argv)
{
uint32_t nsec_scale;
! hrtime_t tsc = addr, hrt;
unsigned int *tscp = (unsigned int *)&tsc;
uintptr_t scalehrtimef;
uint64_t scale;
GElf_Sym sym;
! if (!(flags & DCMD_ADDRSPEC)) {
! if (argc != 1)
return (DCMD_USAGE);
! switch (argv[0].a_type) {
case MDB_TYPE_STRING:
! tsc = mdb_strtoull(argv[0].a_un.a_str);
break;
case MDB_TYPE_IMMEDIATE:
! tsc = argv[0].a_un.a_val;
break;
default:
return (DCMD_USAGE);
}
}
--- 803,837 ----
/*ARGSUSED*/
static int
scalehrtime_cmd(uintptr_t addr, uint_t flags, int argc, const mdb_arg_t *argv)
{
uint32_t nsec_scale;
! hrtime_t tsc = addr, hrt, tsc_last, base, mult = 1;
unsigned int *tscp = (unsigned int *)&tsc;
uintptr_t scalehrtimef;
uint64_t scale;
GElf_Sym sym;
+ int expected = !(flags & DCMD_ADDRSPEC);
+ uint_t absolute = FALSE, relative = FALSE;
! if (mdb_getopts(argc, argv,
! 'a', MDB_OPT_SETBITS, TRUE, &absolute,
! 'r', MDB_OPT_SETBITS, TRUE, &relative, NULL) != argc - expected)
return (DCMD_USAGE);
! if (absolute && relative) {
! mdb_warn("can't specify both -a and -r\n");
! return (DCMD_USAGE);
! }
!
! if (expected == 1) {
! switch (argv[argc - 1].a_type) {
case MDB_TYPE_STRING:
! tsc = mdb_strtoull(argv[argc - 1].a_un.a_str);
break;
case MDB_TYPE_IMMEDIATE:
! tsc = argv[argc - 1].a_un.a_val;
break;
default:
return (DCMD_USAGE);
}
}
*** 827,842 ****
if (mdb_readsym(&nsec_scale, sizeof (nsec_scale), "nsec_scale") == -1) {
mdb_warn("couldn't read 'nsec_scale'");
return (DCMD_ERR);
}
scale = (uint64_t)nsec_scale;
hrt = ((uint64_t)tscp[1] * scale) << NSEC_SHIFT;
hrt += ((uint64_t)tscp[0] * scale) >> (32 - NSEC_SHIFT);
! mdb_printf("0x%llx\n", hrt);
return (DCMD_OK);
}
/*
--- 856,899 ----
if (mdb_readsym(&nsec_scale, sizeof (nsec_scale), "nsec_scale") == -1) {
mdb_warn("couldn't read 'nsec_scale'");
return (DCMD_ERR);
}
+ if (mdb_readsym(&tsc_last, sizeof (tsc_last), "tsc_last") == -1) {
+ mdb_warn("couldn't read 'tsc_last'");
+ return (DCMD_ERR);
+ }
+
+ if (mdb_readsym(&base, sizeof (base), "tsc_hrtime_base") == -1) {
+ mdb_warn("couldn't read 'tsc_hrtime_base'");
+ return (DCMD_ERR);
+ }
+
+ /*
+ * If our time is greater than half of tsc_last, we will take our
+ * delta against tsc_last, convert it, and add that to (or subtract it
+ * from) tsc_hrtime_base. This mimics what the kernel actually does
+ * in gethrtime() (modulo the tsc_sync_tick_delta) and gets us a much
+ * higher precision result than trying to convert a large tsc value.
+ */
+ if (absolute || (tsc > (tsc_last >> 1) && !relative)) {
+ if (tsc > tsc_last) {
+ tsc = tsc - tsc_last;
+ } else {
+ tsc = tsc_last - tsc;
+ mult = -1;
+ }
+ } else {
+ base = 0;
+ }
+
scale = (uint64_t)nsec_scale;
hrt = ((uint64_t)tscp[1] * scale) << NSEC_SHIFT;
hrt += ((uint64_t)tscp[0] * scale) >> (32 - NSEC_SHIFT);
! mdb_printf("0x%llx\n", base + (hrt * mult));
return (DCMD_OK);
}
/*
*** 998,1009 ****
{ "pfntomfn", ":", "convert physical page to hypervisor machine page",
pfntomfn_dcmd },
{ "mfntopfn", ":", "convert hypervisor machine page to physical page",
mfntopfn_dcmd },
{ "memseg_list", ":", "show memseg list", memseg_list },
! { "scalehrtime", ":",
! "scale an unscaled high-res time", scalehrtime_cmd },
{ "x86_featureset", NULL, "dump the x86_featureset vector",
x86_featureset_cmd },
#ifdef _KMDB
{ "sysregs", NULL, "dump system registers", sysregs_dcmd },
#endif
--- 1055,1066 ----
{ "pfntomfn", ":", "convert physical page to hypervisor machine page",
pfntomfn_dcmd },
{ "mfntopfn", ":", "convert hypervisor machine page to physical page",
mfntopfn_dcmd },
{ "memseg_list", ":", "show memseg list", memseg_list },
! { "scalehrtime", ":[-a|-r]", "scale an unscaled high-res time",
! scalehrtime_cmd, scalehrtime_help },
{ "x86_featureset", NULL, "dump the x86_featureset vector",
x86_featureset_cmd },
#ifdef _KMDB
{ "sysregs", NULL, "dump system registers", sysregs_dcmd },
#endif