I've noticed some erratic behavior while testing the X86_64 version
of monotonic_clock().
While spinning in a loop reading monotonic clock values (pinned to a
single cpu) I noticed that the difference between subsequent values
occasionally went negative (time going backwards).
I found that in the following code:
this_offset = get_cycles_sync();
/* FIXME: 1000 or 1000000? */
--> offset = (this_offset - last_offset)*1000 / cpu_khz;
}
return base + offset;
the offset sometimes turns out to be 0, even though
this_offset > last_offset.
+Added fix From: Toyo Abe <toyoa@mvista.com>
The x86_64-mm-monotonic-clock.patch in 2.6.18-rc4-mm2 made a change to
the updating of monotonic_base. It now uses cycles_2_ns().
I suggest that a set_cyc2ns_scale() should be done prior to the setup_irq().
Because cycles_2_ns() can be called from the timer ISR right after the irq0
is enabled.
Signed-off-by: Toyo Abe <toyoa@mvista.com>
Signed-off-by: Dimitri Sivanich <sivanich@sgi.com>
Signed-off-by: Andi Kleen <ak@suse.de>
cbf9b4bb76