While trying to gain some insight into a disk issue, I found that blktrace/blkparse was giving me bogus traces -- I was seeing requests complete before they were even dispatched or queued even! I had thought that maybe this was an issue with SMP on the box, but when running with 'maxcpus=1', it told me that my 53 second test run only took 3.5 seconds. I started tracking this down, and upon looking at cpu_clock(), and found that it uses sched_clock(), which is based on jiffies. At this point I had an ahah! moment and remembered that I had NO_HZ enabled. Turning that off got blktrace to report the proper time for the test run. I'm not sure of the proper fix, nor am I sure I'm going to have much time to track this down at the momenet, but I thought someone should know. -- Dave Dillow National Center for Computational Science Oak Ridge National Laboratory (865) 241-6602 office - To unsubscribe from this list: send the line "unsubscribe linux-btrace" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
