Re: [patch 0/3] [Announcement] Performance Counters for Linux

David Miller
2008-12-05T08:49:32Z

From: Ingo Molnar <mingo@elte.hu>
Date: Fri, 5 Dec 2008 09:42:33 +0100

> Please let me repeat: it's a _fundamental_ thesis of performance
> instrumentation to not disturb the monitored context. Your insistence on
> _stopping_ the monitored task breaks that fundamental axiom!

This is only a problem if you make your measurement quantums too
small.

Furthermore, there are multiple registers and states to update
atomically when a perf counter overflows. You're read/write thing
just doesn't cut it, especially for certain kinds of hardware.

It's really a utopian view of the world. :)