mirror/freebsd
1
0
Fork 0
mirror of https://git.FreeBSD.org/src.git synced 2025-01-04 12:52:15 +00:00
Code Issues Releases Activity

Introduce kern.timecounter.smp_tsc_adjust tunable (disabled by default) and

Browse Source 
respective functionality, allowing to synchronize TSC on APs to match BSP's
during boot.  It may be unsafe in general case due to theoretical chance of
later drift if CPUs are using different clock rate or source, but it allows
to use TSC in some cases when difference caused by some initialization bug,
while TSCs are known to increment synchronously.

Reviewed by:	jimharris, kib
MFC after:	1 month
This commit is contained in:
Alexander Motin 2013-04-18 17:07:04 +00:00
parent 175b3f31d3
commit b2c63698d4
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=249625
1 changed files with 60 additions and 3 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

63
sys/x86/x86/tsc.c
View File

@ -65,6 +65,11 @@ int smp_tsc;
SYSCTL_INT(_kern_timecounter, OID_AUTO, smp_tsc, CTLFLAG_RDTUN, &smp_tsc, 0,
"Indicates whether the TSC is safe to use in SMP mode");
TUNABLE_INT("kern.timecounter.smp_tsc", &smp_tsc);
int smp_tsc_adjust = 0;
SYSCTL_INT(_kern_timecounter, OID_AUTO, smp_tsc_adjust, CTLFLAG_RDTUN,
&smp_tsc_adjust, 0, "Try to adjust TSC on APs to match BSP");
TUNABLE_INT("kern.timecounter.smp_tsc_adjust", &smp_tsc_adjust);
#endif
static int tsc_shift = 1;
@ -403,25 +408,77 @@ comp_smp_tsc(void *arg)
}
}
static void
adj_smp_tsc(void *arg)
{
uint64_t *tsc;
int64_t d, min, max;
u_int cpu = PCPU_GET(cpuid);
u_int first, i, size;
first = CPU_FIRST();
if (cpu == first)
return;
min = INT64_MIN;
max = INT64_MAX;
size = (mp_maxid + 1) * 3;
for (i = 0, tsc = arg; i < N; i++, tsc += size) {
d = tsc[first * 3] - tsc[cpu * 3 + 1];
if (d > min)
min = d;
d = tsc[first * 3 + 1] - tsc[cpu * 3 + 2];
if (d > min)
min = d;
d = tsc[first * 3 + 1] - tsc[cpu * 3];
if (d < max)
max = d;
d = tsc[first * 3 + 2] - tsc[cpu * 3 + 1];
if (d < max)
max = d;
}
if (min > max)
return;
d = min / 2 + max / 2;
__asm __volatile (
"movl $0x10, %%ecx\n\t"
"rdmsr\n\t"
"addl %%edi, %%eax\n\t"
"adcl %%esi, %%edx\n\t"
"wrmsr\n"
: /* No output */
: "D" ((uint32_t)d), "S" ((uint32_t)(d >> 32))
: "ax", "cx", "dx", "cc"
);
}
static int
test_tsc(void)
{
uint64_t *data, *tsc;
u_int i, size;
u_int i, size, adj;
if ((!smp_tsc && !tsc_is_invariant) || vm_guest)
return (-100);
size = (mp_maxid + 1) * 3;
data = malloc(sizeof(*data) * size * N, M_TEMP, M_WAITOK);
adj = 0;
retry:
for (i = 0, tsc = data; i < N; i++, tsc += size)
smp_rendezvous(tsc_read_0, tsc_read_1, tsc_read_2, tsc);
smp_tsc = 1; /* XXX */
smp_rendezvous(smp_no_rendevous_barrier, comp_smp_tsc,
smp_no_rendevous_barrier, data);
if (!smp_tsc && adj < smp_tsc_adjust) {
adj++;
smp_rendezvous(smp_no_rendevous_barrier, adj_smp_tsc,
smp_no_rendevous_barrier, data);
goto retry;
}
free(data, M_TEMP);
if (bootverbose)
printf("SMP: %sed TSC synchronization test\n",
smp_tsc ? "pass" : "fail");
printf("SMP: %sed TSC synchronization test%s\n",
smp_tsc ? "pass" : "fail",
adj > 0 ? " after adjustment" : "");
if (smp_tsc && tsc_is_invariant) {
switch (cpu_vendor_id) {
case CPU_VENDOR_AMD: