From mboxrd@z Thu Jan 1 00:00:00 1970 From: "John Hawkes" Date: Thu, 20 Nov 2003 22:14:36 +0000 Subject: Re: [PATCH] - sched_clock() broken for ia64 SN platform Message-Id: List-Id: References: In-Reply-To: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: linux-ia64@vger.kernel.org From: "john stultz" > 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