diff options
Diffstat (limited to 'sys/i386')
| -rw-r--r-- | sys/i386/conf/NOTES | 5 | ||||
| -rw-r--r-- | sys/i386/i386/tsc.c | 25 |
2 files changed, 18 insertions, 12 deletions
diff --git a/sys/i386/conf/NOTES b/sys/i386/conf/NOTES index 6b0fb42..46bebdd 100644 --- a/sys/i386/conf/NOTES +++ b/sys/i386/conf/NOTES @@ -247,11 +247,6 @@ options CLK_CALIBRATION_LOOP options CLK_USE_I8254_CALIBRATION options CLK_USE_TSC_CALIBRATION -# One some SMP mainboards, the TSCs can be used in SMP mode due to -# them being synchronized. This can significantly reduce the context -# switch cost. -options SMP_TSC - ##################################################################### # MISCELLANEOUS DEVICES AND OPTIONS diff --git a/sys/i386/i386/tsc.c b/sys/i386/i386/tsc.c index abc6a93..36ae1b9 100644 --- a/sys/i386/i386/tsc.c +++ b/sys/i386/i386/tsc.c @@ -30,11 +30,12 @@ #include <sys/param.h> #include <sys/systm.h> +#include <sys/sysctl.h> #include <sys/time.h> #include <sys/timetc.h> #include <sys/kernel.h> -#include <sys/sysctl.h> #include <sys/power.h> +#include <sys/smp.h> #include <machine/clock.h> #include <machine/md_var.h> #include <machine/specialreg.h> @@ -43,6 +44,13 @@ uint64_t tsc_freq; int tsc_is_broken; u_int tsc_present; +#ifdef SMP +static int smp_tsc; +SYSCTL_INT(_kern_timecounter, OID_AUTO, smp_tsc, CTLFLAG_RD, &smp_tsc, 0, + "Indicates whether the TSC is safe to use in SMP mode"); +TUNABLE_INT("kern.timecounter.smp_tsc", &smp_tsc); +#endif + static unsigned tsc_get_timecount(struct timecounter *tc); static struct timecounter tsc_timecounter = { @@ -77,14 +85,17 @@ init_TSC(void) if (bootverbose) printf("TSC clock: %ju Hz\n", (intmax_t)tsc_freq); -#if defined(SMP) && !defined(SMP_TSC) +#ifdef SMP /* - * We can not use the TSC in SMP mode, until we figure out a - * cheap (impossible), reliable and precise (yeah right!) way - * to synchronize the TSCs of all the CPUs. - * Modern SMP hardware has the ACPI timer and we use that. + * We can not use the TSC in SMP mode unless the TSCs on all CPUs + * are somehow synchronized. Some hardware configurations do + * this, but we have no way of determining whether this is the + * case, so we do not use the TSC in multi-processor systems + * unless the user indicated (by setting kern.timecounter.smp_tsc + * to 1) that he believes that his TSCs are synchronized. */ - return; + if (mp_ncpus > 1 && !smp_tsc) + return; #endif /* |
