Am Dienstag, 10. September 2013, 12:38:56 schrieb John Stultz: Hi John,
>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. Thank you for the explanation. Is there any trigger that is fired at fs_init time that one can read? Thanks > >thanks >-john Ciao Stephan -- 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/
