On Tue, Sep 10, 2013 at 4:31 AM, Stephan Mueller <smuel...@chronox.de> wrote: > Hi, > > /dev/random uses the get_cycles() function to obtain entropy in addition to > jiffies and the event value of hardware events. > > Typically the high-resolution timer of get_cycles delivers the majority of > entropy, because the event value is quite deterministic and jiffies are very > coarse. > [snip] > The following patch uses the clocksource clock for a time value in case > get_cycles returns 0. As clocksource may not be available during boot time, a > flag is introduced which allows random.c to check the availability of > clocksource. > [snip] > diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c > index 48b9fff..75b1613 100644 > --- a/kernel/time/timekeeping.c > +++ b/kernel/time/timekeeping.c > @@ -35,6 +35,7 @@ static struct timekeeper timekeeper; > static DEFINE_RAW_SPINLOCK(timekeeper_lock); > static seqcount_t timekeeper_seq; > static struct timekeeper shadow_timekeeper; > +static bool timekeeper_enabled = 0; > > /* flag for if timekeeping is suspended */ > int __read_mostly timekeeping_suspended; > @@ -833,8 +834,15 @@ void __init timekeeping_init(void) > > write_seqcount_end(&timekeeper_seq); > raw_spin_unlock_irqrestore(&timekeeper_lock, flags); > + timekeeper_enabled = 1; > } >
So the end of timekeeping_init() may not be what you want here. This only means we've started up the timekeping core with only the default clocksource (with only few exceptions, this is almost always jiffies). Then as clocksource drivers are initialized, they are registered and the timekeeping core will switch over to the best available clocksource. Also, to avoid the churn at boot of switching to every clocksource registered, we queue them up and wait until fs_init time to switch to whatever is the best available then. So its likely with this patch that the systems all still end up using jiffies for their clocksource at least until fs_init time. thanks -john -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
