Hello.
Herbert Valerio Riedel wrote:
On Tue, 2006-05-16 at 01:35 +0400, Sergei Shtylyov wrote:
I just switched to 2.6.16.16 from 2.6.14 on a Au1550. I enabled
CONFIG_PRINTK_TIME, and for some reason jiffies doesn't start out near
zero like it does on x86. The first printk() always seems to have a
time of 4284667.296000.
jiffies_64 and wall_jiffies gets initialized to INITIAL_JIFFIES, but
I'm not sure where jiffies is initialized. INITIAL_JIFFIES is -300*HZ
(with some weird casting)
Yes, the casting is weird. I somewat doubt that:
#define INITIAL_JIFFIES ((unsigned long)(unsigned int) (-300*HZ))
u64 jiffies_64 = INITIAL_JIFFIES;
can do the trick of wrapping around 5 mins after boot on x86... :-/
jfyi, starting with an offset of -300 seconds is done on purpose, to
expose bugs in drivers which don't handle wrapping of the jiffies;
Oh, thank you. I've read that in the source code. :-)
and the trick to get printk to start at offset 0 is either define a
arch-specific printk_clock() function (it's a weak symbol in
kernel/printk.c) or like more drivers to it, to provide a sched_clock()
(which is used by the default printk_clock() function) implementation
which starts at offset 0...
sched_clock() defined in arch/i386/kernel/timers/timer_tsc.c can hardly
provide 0-based time if it's using TSC (at least I can't see where the TSC is
cleared). Even if it's not using TSC, jiffies_64 is not 0-based as we saw, and
neither it's set to -300 secs because of the double cast to ulong and then to
u64 which should clear the high word. Probably something somewhere clears TSC
but I can see the related code only in arch/i386/kernel/smpboot.c...
regards,
hvr
WBR, Sergei
