Re: [PATCH] - sched_clock() broken for ia64 SN platform

From: John Hawkes <hawkes_at_sgi.com>
Date: 2003-11-21 09:14:36
From: "john stultz" <johnstul@us.ibm.com>
> I too was confused why per-cpu start and stop times were not just used
> for this high-res accounting. I'm not sure I can look into it now, but
> I'd be interested to hear why we'd compare timestamps across cpus
> (rather then just use time deltas calculated on a single cpu).

sched_clock() and task->timestamp are used in two different ways.  One is for
supposedly high-res accounting.  The other is for can_migrate_task(), called
during load-balancing, to determine if the process has slept long enough to
consider it to no longer be cache-hot.  It's this latter use that suffers from
a drifty timebase.

John Hawkes


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Received on Thu Nov 20 17:15:51 2003

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