Complexity of dealing with all the random issues that have plagued TSC in different cpus over the years definitely seems to be a problem. I have one more idea on how we might be able to use TSC locally and still have confidence that we can merge local cpu buffers into a consistent stream. What if we read the HPET occasionally (once per second?) and add a record to our per-cpu buffer with the value of the HPET. That would give us a periodic cross-check of each cpus TSC against real time so that a "smart" post-processor can sanity check the log entries at regular intervals. It doesn't deal with the truly insane TSC behaivours (like stopping completely in certain C states, or varying frequency) ... but it would at least be able to reliably detect these forms of insanity. We need periodic entries added to the buffer anyway to make sure we can detect rollover since we don't want waste space in log records with a full width TSC value. -Tony -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
