Messages in this thread | | | Date | Tue, 20 Sep 2005 12:02:34 +0200 | From | Pierre Ossman <> | Subject | sched_clock() has poor resolution |
| |
I've been trying to hunt down a HZ bug and as part of that I thought having printk timestamps would be nice. But too much dismay I noticed that I couldn't get very good resolution out of these.
The problem turned out to be that sched_clock() uses jiffies as a time source. It will only use the TSC if that's the primary time source of the system. But since I have a PM timer that is given priority.
So I see two solutions here:
* Let sched_clock() follow the time source. Don't have it coupled to the TSC.
* Init the TSC even though it isn't used for anything but sched_clock().
The first solution might have problems if one of the "better" timers are slow as hell to read and the second if there is some assumed dependency between sched_clock() and the primary timer. I'm blisfully ignorant of this area so input is welcome.
Rgds Pierre - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |