diff options
Diffstat (limited to 'drivers/lguest/lguest.c')
| -rw-r--r-- | drivers/lguest/lguest.c | 52 |
1 files changed, 36 insertions, 16 deletions
diff --git a/drivers/lguest/lguest.c b/drivers/lguest/lguest.c index 3386b0e..1bc1546 100644 --- a/drivers/lguest/lguest.c +++ b/drivers/lguest/lguest.c @@ -643,21 +643,42 @@ static void __init lguest_init_IRQ(void) * Time. * * It would be far better for everyone if the Guest had its own clock, but - * until then it must ask the Host for the time. + * until then the Host gives us the time on every interrupt. */ static unsigned long lguest_get_wallclock(void) { - return hcall(LHCALL_GET_WALLCLOCK, 0, 0, 0); + return lguest_data.time.tv_sec; } -/* If the Host tells us we can trust the TSC, we use that, otherwise we simply - * use the imprecise but reliable "jiffies" counter. */ static cycle_t lguest_clock_read(void) { + unsigned long sec, nsec; + + /* If the Host tells the TSC speed, we can trust that. */ if (lguest_data.tsc_khz) return native_read_tsc(); - else - return jiffies; + + /* If we can't use the TSC, we read the time value written by the Host. + * Since it's in two parts (seconds and nanoseconds), we risk reading + * it just as it's changing from 99 & 0.999999999 to 100 and 0, and + * getting 99 and 0. As Linux tends to come apart under the stress of + * time travel, we must be careful: */ + do { + /* First we read the seconds part. */ + sec = lguest_data.time.tv_sec; + /* This read memory barrier tells the compiler and the CPU that + * this can't be reordered: we have to complete the above + * before going on. */ + rmb(); + /* Now we read the nanoseconds part. */ + nsec = lguest_data.time.tv_nsec; + /* Make sure we've done that. */ + rmb(); + /* Now if the seconds part has changed, try again. */ + } while (unlikely(lguest_data.time.tv_sec != sec)); + + /* Our non-TSC clock is in real nanoseconds. */ + return sec*1000000000ULL + nsec; } /* This is what we tell the kernel is our clocksource. */ @@ -665,8 +686,11 @@ static struct clocksource lguest_clock = { .name = "lguest", .rating = 400, .read = lguest_clock_read, + .mask = CLOCKSOURCE_MASK(64), + .mult = 1, }; +/* The "scheduler clock" is just our real clock, adjusted to start at zero */ static unsigned long long lguest_sched_clock(void) { return cyc2ns(&lguest_clock, lguest_clock_read() - clock_base); @@ -742,24 +766,21 @@ static void lguest_time_init(void) set_irq_handler(0, lguest_time_irq); /* Our clock structure look like arch/i386/kernel/tsc.c if we can use - * the TSC, otherwise it looks like kernel/time/jiffies.c. Either way, - * the "rating" is initialized so high that it's always chosen over any - * other clocksource. */ + * the TSC, otherwise it's a dumb nanosecond-resolution clock. Either + * way, the "rating" is initialized so high that it's always chosen + * over any other clocksource. */ if (lguest_data.tsc_khz) { lguest_clock.shift = 22; lguest_clock.mult = clocksource_khz2mult(lguest_data.tsc_khz, lguest_clock.shift); - lguest_clock.mask = CLOCKSOURCE_MASK(64); lguest_clock.flags = CLOCK_SOURCE_IS_CONTINUOUS; - } else { - /* To understand this, start at kernel/time/jiffies.c... */ - lguest_clock.shift = 8; - lguest_clock.mult = (((u64)NSEC_PER_SEC<<8)/ACTHZ) << 8; - lguest_clock.mask = CLOCKSOURCE_MASK(32); } clock_base = lguest_clock_read(); clocksource_register(&lguest_clock); + /* Now we've set up our clock, we can use it as the scheduler clock */ + paravirt_ops.sched_clock = lguest_sched_clock; + /* We can't set cpumask in the initializer: damn C limitations! Set it * here and register our timer device. */ lguest_clockevent.cpumask = cpumask_of_cpu(0); @@ -996,7 +1017,6 @@ __init void lguest_init(void *boot) paravirt_ops.time_init = lguest_time_init; paravirt_ops.set_lazy_mode = lguest_lazy_mode; paravirt_ops.wbinvd = lguest_wbinvd; - paravirt_ops.sched_clock = lguest_sched_clock; /* Now is a good time to look at the implementations of these functions * before returning to the rest of lguest_init(). */ |