Re: [PATCH 1/4] x86_64: (SPARSE_VIRTUAL doubles sparsemem speed)

William Lee Irwin III
2007-04-09T16:40:52Z

On Sat, Apr 07, 2007 at 03:06:13PM -0700, Christoph Lameter wrote:
> +/*
> + * Performance Counters and Measurement macros
> + * (C) 2005 Silicon Graphics Incorporated
> + * by Christoph Lameter <clameter@sgi.com>, April 2005
> + *
> + * Counters are calculated using the cycle counter. If a process
> + * is migrated to another cpu during the measurement then the measurement
> + * is invalid.
> + *
> + * We cannot disable preemption during measurement since that may interfere
> + * with other things in the kernel and limit the usefulness of the counters.
> + */

Whatever's going on with the rest of this, I really like this
instrumentation patch. It may be worthwhile to allow pc_start() to be
overridden so things like performance counter MSR's are usable, but
the framework looks very useful.

-- wli