In kernel/timer.c we currently have jiffies_64, of which jiffies is
the least-significant long-sized piece, and wall_jiffies. The code
that updates them looks like this (from kernel/timer.c):
static inline void update_times(void)
{
unsigned long ticks;
ticks = jiffies - wall_jiffies;
if (ticks) {
wall_jiffies += ticks;
update_wall_time(ticks);
}
calc_load(ticks);
}
/*
* The 64-bit jiffies value is not atomic - you MUST NOT read it
* without sampling the sequence number in xtime_lock.
* jiffies is defined in the linker script...
*/
void do_timer(struct pt_regs *regs)
{
jiffies_64++;
update_times();
softlockup_tick(regs);
}
In other places there is code that uses (jiffies - wall_jiffies).
However I can't see any way that jiffies and wall_jiffies could ever
be different (except for a few nanoseconds while executing the code
above). I also can't see any way that `ticks' could ever be anything
other than 1.
Is the wall_jiffies stuff just a leftover from days when we used to do
timekeeping from a softirq? Or am I missing something fundamental?
Thanks,
Paul.
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